I'm planning on signing up DH for an RMN account too. It will be linked to his email address, with his credit cards linked to his RMN account. Since you could potentially get $20 back on the $50 Disney GC purchase by using 2 RMN accounts, I would try to split tender, you just need to tell the cashier you want to split the payment on two cards. Put $25 on one of the CCs in your account and $25 on one of the CCs in your DH's account. If you're uncertain, I would just ask the cashier if that is something you can do before entering into the transaction. I don't know if digital wallet payments work since those create a different card number...
I would make them different CCs too since I read somewhere that it runs on the Empyr network which recognizes which cards are attached to which programs (like Dosh, dining programs, etc.) and you can't duplicate a CC in different programs. Has anyone else run into that? I've also noticed that VGC and MCGC don't work in the RMN app to link CC.