Disclaimer, I'm not a contractor but have a fair amount of rebuilding here in Taxyafornia. I've always gotten along well with the Build Department Inspectors. I choose to everything 'with permit'.
Assuming that your hanger is well enough insulated that heating it would work well, here is what I recommend. It's worth at least two cents, maybe three!
Can you accept a NO as an answer from the building department, local hanger manager, fire department, airport authorities, etc? If the answer is that you can accept a NO, then I recommend the following. You may stir up a hornets nest of unofficial opinion and official government opinion but you can see it through. Opinion is worth little so get it in writing.
In my opinion, it is wise to play it by the book. You will find that almost everyone has an opinion but I wouldn't install anything that the Building and Fire Department Inspectors wouldn't approve. You need to be standing in firm legal ground before you pay anyone to start your project.
First, check around the airport and gather as much intel as you can from those who have already installed heaters. Ask questions - including, when did you install this heater set up? Which contractor installed it? How much did it 'really cost'. Let those other hanger owners know that you intend to have a 'permitted installation'. Find out if a heater is allowed in your type of hanger.
Find a well liked heating/cooling contractor in your area, preferably one who has done a heater of the same type in a hanger located in whichever city or county issues the permit and employs the building inspectors for your area. Make sure that your contractor is legit and that he has a good relationship with the Build Department and it's inspectors (Very important).
Ask that contractor to show you you an example of his/her work. When you get to the 'show and tell' location, ask that contractor to show you the actual permit for that job. My experience here in taxyafornia, the permit to build/install, modify a commercial building must be displayed inside of the building. As a Fire Inspector Inspector for the Los Angeles Fire Department, I always looked for that permit. In theory, the permit lends a certain amount of legitimacy to the construction/modification of the building.
Get several bids if possible. Tell the contractors exactly what you need - how much heat, etc. If you don't have an answer to that question then you need to do further intel at the airport if possible. Listen carefully to what the prospective contractor has to say. I assume that you don't want a system that would take your hanger from 40 degrees to 45 degrees. If you want 40 to 65 then tell the contractor up front. Is that added 25 degree increase even possible inside of your hanger?
Don't necessarily take the lowest bid. Take into consideration that the general public thinks that anyone who can afford an airplane and a hanger is 'rich'. You may find that the various bids vary considerably. Find out why.
After doing your homework as above and it all looks good, take a trip to the Building Department and talk to the Inspectors and the Boss Inspector there. Make sure that what you want to do is ok with them. Tell them which contractor that you have 'tentatively chosen' and watch their body language as well as listen to what the say. They probably can't give you a definitive yes or no about your chosen contractor but definitely take a shot at getting at least a little feedback from them. Body language may or may not be a reliable indicator but you are still gathering intel - right? Make it clear to them that you are doing a 'permitted' job.
If everything is good then sit down with your contractor and get everything down in writing. When you do this, remember that he is the 'expert' but you are 'paying him' to do your work. Insist on seeing 'AN APPROVED SET OF PLANS FROM THE BUILDING DEPARTMENT'. Have the contractor make a copy for your records. This may come in very usefully in the future. If I wanted to buy your hanger, I would insist on seeing an approved (approval stamped on the plans) set of plans before we sit down and talk $$$$$.
Assume nothing!!! Get everything in writing. I always try to get a firm date of start and completion. Some contractors tend to take on too many jobs and work at a few of them at a time while essentially ignoring the rest for later. Make it clear that you want a 'permitted' job.
If you can't accept a NO from the various government entities, then good luck to you. A bootlegged heater may be cheaper but you may be sorry later. Remember, you are renting out your 'commercial' hanger. Your insurance person may want to see the permits!
Additional thought - since I live here in Taxyafornia, I know nothing about heating the hanger with hot water pipes concreted into the floor but I wonder if this is a valid solution to your dilemma? Could a contractor lay piping over your existing hanger floor and then concrete over the piping? My guess is that you would have to have an additional layer of concrete of at least 6-8" but I really don't like this solution because I don't know if would work well. How do you 'anchor' the second concrete floor to the first one?
Instead, you would likely have to tear up the existing floor in order to install this type of floor heating correctly. This solution would place the heating device outside of your hanger - but I am guessing that this alternative may be quite expensive as you already have a concrete hanger floor. Right?
As I said, all of the above is worth maybe at least 3 cents but considering what it cost you to read it, it's a bargain! As an aside, I am very interested to hear which solution you choose and how well you did. Best to you.