Yes, this is how I determine rib doneness, although I wouldn’t worry about it until the 5- or even 6-hour mark if you are cooking at 225. The meat should be pulling away from the tips of the bones a little bit and you should be able to bend the rack pretty easily (but you don’t want the bones to come out or the rack to break in half when you try to bend it - if those things happen, you’ve cooked them too long).
As for a mop or baste, @bbqboy is correct - it really just adds another layer of flavor and prevents excess surface drying. I don’t generally use sauce of any kind on my ribs, but dry rub alone isn’t always quite enough flavor for me, so the basting sauce gives me just enough of an extra flavor boost (plus the butter adds a little bit of succulent crispness to the spice rub bark). My DH does like BBQ sauce on his ribs so I sometimes baste a couple of racks with BBQ close to the end of cooking just for him (goes on after the butter baste), but more often he just dips individual ribs into sauce on his plate as he sees fit.
