Can mask Scent, and Camoflage be used during combat or on PCFollow

Just thinking about going the ranger route and was wondering wether these abilites can be used to hide after you are already envolved in combat. I would also like to know wether or not these abilities can aid you at all against player characters in PvP. Obviosly it would be great if a Player chacter in combat was more difficult to target in combat when camoflaged, in PVP.

-The Force envelops all things with out distinction to Good or Evil-