If you believe the pot will split, one hi, one low, and it is a ring game, then raising will only cost you money. As the pots get bigger, the rake gets bigger!
If it is a tourney style game, then raising in a split pot won't cost you anything except when you get quartered.
example; you have nut low, another has nut low, a 3rd player has the hi
board shows 679T8 rainbow and they came in that order.
Hi has JQ8x, you and another have A2. The high hand has had the nuts since the turn, and only got called. He figures you both for low hands since you did not raise early (most likely). He is pushing, you are being dragged. When the low hits, highs nut hi got better, and of course he is raising, as there will always be a hi hand in Omaha8, and he has the nuts, if either low now raises, the other low will call, and the hi will continue to raise, etc etc till something maxes.
For simplicity use $100 bets.
For every $100 you put in at this point, if you get quartered, you will only get $75 of it back.
The sole hi hand will get $150 for his $100 in a three way split pot where he is the only hi.
That is tourney style, no rake there.
In a ring game take out a 5%-10% rake (depending on location) and your $75 turns into $67.50 - $71.50 (again depending on location).
Moral of this is to learn pot control.