You mean your opponents never fold? Well, in this case play only strong starting
hands, which hit the flops in awesome ways. Bet/call your monster draws and always try to acquire the nuts. If they never fold, you'll be able to extract maximum value when you have it, so you can afford to be more selective about your starting hands. Except when you are playing some short stack 6-max turbo tournament... The variance in Omaha tournaments is terrible when you can't afford to wait for good hands.
There are less pure
bluffing opportunities in Omaha, 'cause it's rather rare to hold complete air. Most bluffs are semi-bluffs.
Many players overvalue their hands, though, so not everyone is aggressive because of aggressive playstyle.
Against complete maniacs it's pretty tough, 'cause they don't give you good
odds to draw post-flop. If they bet every hand, I'd probably try to isolate them with a good pre-flop hand like one containing AA or double-pair. These are good 1v1 hands. If there are several maniacs... expect high variance :|