also, iirc, floats' comparison is compatible with signed integers' comparison due to representation?

so just using cuda's AtomicMin for ints would be enough

Positive finite floats compare like ints. If you can have negative values, things get slightly more complicated, since they use sign-magnitude (you basically shift the sign bit to the right and use that as an XOR mask on all the other bits). If you need to care about -0.0 == +0.0 and NaN != NaN, most bets are off. :-)