As a few have said, the people working on getting PR:ARMA up and running are all from the OPF/ARMA community so there will be no effect on the development of BF2

R. If anything, certain bits will be sped up. For example, if we (PR:ARMA) made a Mastiff or Jackal, it would save PR:BF2 having to make one if they wanted to include either vehicle in a future PR release.
in terms of just 4 or 5 of us making the Mod for ARMA, It will move much faster than it did for BF2 because alot of the assets have already been made (as an example almost the entire british faction is in there already). ARMA's engine is also far easier to mod for than BF2's. Something that might take PR a week to implement in BF2 could take a day for ARMA. Also I doubt we will be a team of 4 or 5 for too long.
Anyway, we don't intend to split the community in any way. Personally I play both ARMA and PR:BF2 as they provide different expeirences for me. Even with the PR template in ARMA both expeirences will still be different.