I married an American Muslim. Our respective faiths (my lack thereof) were never an issue. Early in my adult life, I was a Bible-thumping theist and my spouse was an Atheist. Again, it was never a problem.
Where I would have a problem with a JW is that's a cult, and I can only stretch my "to each their own" so far ... that's tooooo far a reach (Scientology, Mormons, 7th Dayers, JW, Urantia followers, etc., are simply too far removed for me.)
I cannot see how the Atheist could respect that JW. I have spoken to many that knock on my door or hang out at malls and I usually leave thinking their are brainwashed. I do not see how I could date someone. Plus if kids are involved it will be a competition.
If the JW is devout (and most of them are because they have to be) I'm hard pressed to imagine how they could get along with ANY sort of non-JW. They are just too controlling and dogmatic, even by fundamentalist standards. You'd have to accept that their religion would be actively working to recruit you or undermine your marriage, those are really the only two options.
Then even if the JW isn't very faithful, there's always the potential for them to "catch fire" so to speak and become devout. And then, watch out. And/or, particularly if they come to the JW faith because they actually buy into any aspect of the dogma, they are vulnerable to all kinds of other religious and quasi-religious "woo", and that's also another way to grow apart.
And of course I haven't even factored children into the equation yet. What atheist would be comfortable with allowing their kids to be indoctrinated into a particularly cultish deviant version of Christianity? And how could they hope for their JW spouse to be sanguine about the kids NOT being indoctrinated?