0) Well no shit, it's got a million dollar budget at the least.

1) Conflicting shaders are possible. And crashes.
2) Pure server says no.
FUN FACT: OA was originally designed to be protocol-compatible with Q3A servers intending to connect to Q3 servers and vice versa, but things couldn't work out technically for various reasons. On the other hand, concerning OAX's additions, it's for the better and benefits from the regression.
FUN FACT 2: People don't really play Q3A anymore, just some promode/defrag stuff for it. If you want to play a Q3 Q3A, you'd have to play Quake Live. UT suffers similar problems with people playing some sniper stuff, Monster hunt stuff, RPG stuff.... Q3's player peak was in 2000, and then the BidForPower DeFraG Excessive CPMA OrangeSmoothie UrbanTerror Quake3Fortress scenes happened and fragmented it all....