The Hi-Point 995-TS falls under the same compliance rules as any other Semi-Auto rifle in New Jersey. You are allowed One (1) "Evil Feature" and since the 995-TS has a pistol grip - that is your EV. The new models are all coming with Threaded barrels, and as such the muzzle nut (or a Muzzle Brake if you so choose) must be pinned and/or welded to make it compliant.
The dealer who told you about the magwell being inside the pistol grip is wrong - period!
You should go back to the dealer you bought it from, and tell them you need it NJ compliant and make them do it; if he says no - find yourself another dealer - fast!