just my two cents;
Your second question for me is a clear No. Don't feck about when you think you can only get half the pot (and indeed get quartered by someone) time to get out pre-flop there...it's a massive leak some players have. Hi/lo is about the scoop and nothing else.
Question one; You should/can raise with a wide range of hands in PLO. Anyone who says "don't raise pre-flop as it's a flop game" is talking out of their arse. (I wanted to slap someone silly when we were at DtD and he kept saying "there's no point raising pre-fop in Omaha") Position obviously determines a lot and essentially any straight hand that's Double Suited
should be raised pre.
5678 DS 6789 DS that sort of stuff. You have a massive hand when holding something like that pre-flop. and, especially in position you should raise with this and get a nice juiy pot. A lot of peope that play PLO play it like they would play hold em and their hand selection is poor, they only raise with suited aces for instance ..or they over play KK rag rag. A hand like the one you have is massive against KK rag rag.
A straight hand like 5678 but 1 suit represented (so

) I feel should still be raised pre when in position..and at some tables when out of position. It's a nice hand..just what you want in PLO (for me anyways)
A rainbow straight is something to be slightly more cautious with but should still be played.
If you raise with all of the above hands and not just AAXX DS or monsters like that people have no idea where to place you.
it's not the AAXX hand that will get you a lot of dosh...it's the straights.
just my two cents.