Been a mechanic for 55 years and have yet to see an alternator die because of oil being in it. Had a few that have been soaked in oil and all grimy in and out.
That said I do not believe the oil is good for them.
I would flush it with brake cleaner, ether, or such. Then blow clean air.
Just the day before yesterday I found a pretty good sized oil leak on my vac-pad mounted back up alternator, Lower bolt on co-pilot side. Sealed that leak right away.
My oil consumption had jumped to a quart in 3 hours. Was time to find the problem NOW!!! Had been flying to much and not looking at the belly pan.
There was quite a bit of oil on, around and in the alternator.
I did the flush as good as I could on the outside and through the vent holes and moved on.
I am not worried about it a bit.
An addition to above, I have now flown an additional 4 hours and the oil consumption (leak) is now down to about one in maybe twelve if I read the stick right. Alternator still works fine.
Now your luck may vary Art