Absolutely not. Simply being tolerant / accepting of them wearing around you (even if not visible!) is one degree of acceptance. Being OK with them hanging out in the living room watching TV in a diaper a a T shirt, that's another level. You could get more involved by watching them change, discussing diapers in more detail, or even helping them. (your partner would probably be absolutely floored by an offer to put on or change their diaper) Will you be ok with them using their diaper at all? Or around you? are you OK with changing a used diaper? Again all different levels of participation and you haven't even unbuckled your belt yet.
Diving in deper, again they'd probably be thrilled to see you try a diaper yourself, even if to just put it on and model for them a bit. You might find you really like to cuddle together on the couch with both fo you just in a diaper, t, and some nice white socks
But neither of you should have any expecations in advance. You have to be willing to try something knowing you may not like it. If you don't like it, tell them, and don't feel obligated to that again. And they shouldn't expect you to do anything you find don't like, and shouldn't push you to try something you're not comfortable with. You may surprise yourself though in finding aspects of this you didn't know you were going to enjoy or discover you actually really like.
Diaper changes can be a very intimate thing, a very strong bonding experience, and you may find you really enjoy diapering/changing them, or them you, or both! Just take it in steps so you don't suddenly find yourself in a place you really don't like.
Keep it fun and enjoyable, but don't be afraid to say "I don't want to go any farther than
this just yet..."