"The river brings the 3rd low card and all of a sudden 2 people are raising. Is it safe to assume they both have the nut low and their raising only helps you? "


With low cards on the board consider that one may have made a straight and the other the nut low leaving you...


Unimproved middle sets are generally death in O/8, IMO. Even middle sets that make a boat can be hazardous to your bankroll and should be played somewhat cautiously, again IMO.


"What about the opposite situation, you hit the nut low and someone else comes to life - should you just call hoping to minimize your loss from the 1/4 pot you win? "


To me that depends a lot on which cards make the nut low. If its A2 and the bets and raises start I usually just call because a lot of players will play that with nothing else in their hand and play it strongly too. As the nut low holding moves farther away from A2 (34 for example) I'm more inclined to jam with it. Be aware of where there might be someone holding the nut low and a low straight as well (e.g. board is A256 and they hold 347x).


"I'm playing something like AAQJ, flop is essential a bunch of rags, flop is checked through 6 people, turn is as well, so is the river (no low possible), and I win"


Did you raise preflop to try and thin the field? Essentially a bunch of rags is somewhat nondefinitive. How many of one suit? Any pairs? Any potential straights? Generally if I've raised with aces preflop and have thinned the field down to two or three I'll fire off a bet if in early position or a raise if the board doesn't look too threatening. You have to try and get a handle on what your opponents might be holding and how they react to bets and raises.


Disclaimer: I am NOT an omaha expert, but hopefully one will come along and also answer your questions and critique my answers.