skills from other campaigns

Can skills from one campaign be used in another campaign? If yes, then how do I acquire them in the other campaign? In other words, if I learn a skill in Factions, how/when can I use that skill in Nightfall? This question is PvE only. Thanks.

Yes.

It's quite simple. There is really no difference between skills from different campaigns. Just look at it like you would with any other skills - you get different skills from different places. It's just a matter of taking your Nightfall character over to Factions, obtaining a skill in any way you would normally (trainers/quests/signets of capture/etc) and then go back to Nightfall. Once you learn a skill you can't lose it, barring a couple of temporary skills you're given in a few Factions/NF missions.

Personally, I think the Factions Monk Skills are a cut above Prophecies; Both my Monks have basically Factions only Skill bars; (with the exception of Word of Healing.)

I know your in NF and I dont have enough time there for an realistic comparision; but you might take a peek at them; both in terms of Healing, and Smiting, Ray of Judgment is awesome when you have a toon up to the Capture.