With Limit Omaha/8 easily being my most profitable game to date, I can answer that O8 is profitable without a shadow of a doubt.
You can about break even from the split pots, perhaps make a small profit if the game is very loose, but you make most of your profit from the times that you get 3/4 of the pot or scoop. Therefore, you need to look for situations where enough people are in the pot that a split is worthwhile, situations where you'll split the low but get the high, and situations where you'll scoop a pot.
In particular, look for hands where you'll either probably scoop, or are almost guaranteed to get one end and may improve to get the other - this is known as freerolling as while the hand may not make much profit, you're not risking anything in continuing to play it.
In Limit it's difficult to consistently scoop, but you can find a fair number of situations where you can't lose but can win - so while often you may just split and make only a small amount from the hand, you play enough of them and you will eventually get that scoop, and make your profit. The advantage of O8 is that you can find yourself in hands where you have the low end locked up and someone has, say, a straight, and you have a flush draw, so you will win one way and may win the other sometimes. You should equally try to avoid situations where you are on the wrong end of that and can't win.
Most people making a loss do so because they call with a 2nd-best hand, or play with hands that will only split and may get scooped, and because they play too many hands too far.