....but even if it did it's experimental so it's not required.
... and insurance underwriters quoting RVs don't care or ask about the HP, the prop, or whether the pilot has any of the required endorsements. So that won't matter, so long as he's legal per Part 61.
This one is complex due to CS prop and flaps.
...he probably needs to ride with a CFI in something that has one and get the endorsement.
No such thing. Like Scott pointed out, you only need a complex endorsement if the aircraft has retractable gear, flaps, and a controllable pitch prop (or in the case of a seaplane, flaps and a controllable pitch propeller). Take away one of the 3 and no endorsement required.
For an airplane to be complex it must have ALL THREE...an in-flight controllable pitch prop, flaps and retractable gear.
It doesn't matter - until there is a claim. Just because they didn't ask when you initiated the coverage does not mean they won't deny the claim later if you don't meet the requirements. Ask - do not assume.