do I need to pay attention to OAL or can I verify length with he comparator only?
Comparator only is fine- PROVIDING you're talking about the one bullet...as every bullet type, even of the same weight, has an ogive that's going to hit the lands at a different point.
I determine my loaded bullet length with an OAL gauge, and then set the loaded bullets to length- using the comparator for adjustments- with the seating die to correspond to the jump I'm seeking.
I could not even tell you, the "overall length", of ANY
of the bullets I load for the seven calibers I handload for. It is irrelevant unless there is a restriction related to magazine length.