You can cast Precision on Beholders, so I suspect their ranged attack is considered an "arrow" of sorts. However, I have not been using my Evil Beholders at all and am doing quite well. I still only have Order 2 so I cannot resurrect them via the spell and have to rely on my Inquisitors. Perhaps if I bit the bullet and got Order 3 I'd find them more useful, but I have had no problems crushing enemy stacks all the way up to overpowering so I'm not going to mess with success.
