Reinstalled Rainbow Six 3 on Steam and gonna put back the Raven Shield 2.0 mod, but I also want to install this mod called Ordnance Project:

http://www.youtube.com/watch?v=Nxv866OXbUg

Can the 2 mods work together at the same time?

Yeah its fine, it actually says for Raven Shield 2.0 that you need to install Ordnance :

http://www.moddb.com/games/tom-clancys-rainbow-six-3-raven-shield/news/ravenshield-20-running-ordnance-project


Don't forget, with games that don't come with official mod support on Steam after installing them you need to go into the games properties and remove the automatic updating (Vampire Bloodlines for example). Occasionally what happens if you install a mod is Steam actually re-downloads any modified files and replaces them with the originals.