I have a regular season pass for six flags here in Baltimore Maryland can I use that to get in the water park in Jersey

No my brother in law had Maryland and came to new Jersey but they told him he had to change it cause they have different system

Only if the water park is within the theme park. Our season pass was accepted in NY water park. Both theme and water park are in one.

That is one of the downside of 6 flags. You have to pay different for each 6 flags.

No. Six flags tickets are only for the dry rides. You need to buy separately for hurricane harbor.