I have flown on Nature Air as a passenger but know nothing of pilot jobs or working conditions etc.
I was very impressed with what I saw. A very professional looking outfit, the flights were on time and my online bookings worked out just fine.
The planes seemed well maintained bearing in mind their age.
I would guess that they certainly favour their own nationals for jobs there and I think that they even have their own flight school to hire from.
Go to Costa Rica and check them out, great country, friendly people and well worth a visit.
Good luck and let us know how it goes.
PB