Can you play flamenco on a regular guitar?
You can absolutely play Flamenco on a classical guitar. If you're a beginner then you won't even notice the difference. The only difference is the set up and the wood material used in construction.
Are guitar tabs legal?
If a guitarist works out how to play a song by ear, and tabs his version, then no. The artist should not get royalties. If official tabs are available then they should claim royalties, but if official tabs not available - no royalties.