If you know what they plan on doing with your music once they rerecorded it, and it falls within AJ license terms, then tell them they can go ahead and get a license through Envato. The fact that they rerecord it, does not matter, it could be considered as editing, which is allowed.
If they intended usage is not covered by the license, but you feel there is nothing shady and it won’t hurt you, then licensing the track directly to them is specifically forbidden in Envato help/faq. Now does the exclusivity applies to the recorded material or to the composition? As it’s not specified, a lawyer could argue you’re in your right, should Envato give you hell for this.
But the safest way to go for you is to go through AJ licensing as nothing prevents them to rerecord the track (but no added vocals!).