Of course, toms, snares, kicks, overheads...whatever. If I had enough 421s I would use them on everything. Ok, that's a bit of an exaggeration...but not by much. Maybe not overheads.
The 604 is a fine mic for toms but if I had the money for 4 421s I wouldn't hesitate. I now use 604s for the higher toms and a 421 on floor tom. I have never noticed any more mic bleed on the floor tom.
The 421, in my experience, has a pretty wide pickup pattern compared to many other dynamic mics - that may be why some people talk about the bleed. For me, though, that's one of the mic's strong points - you can put a 421 between 2 toms (or congas, or any other pair of instruments) and you'll get both of them quite nicely.
Especially handy if you're in a limited mic situation due to available channels, mics, cables...or just for taking a more minimalist approach.