Considering you are going to be using full tilt powders, it is absolutely essential to roll crimp into the canelure. That said, the OAL will be determined by the canelure, therefore measuring the OAL is of no importance what so ever. In other words, just roll crimp into the canelure.
If you were using a bullet without a canelure, thus unable to use an effective crimp, those bullets would only be usable with a target load, other wise you would be experiencing a locked up wheel gun real quick and in a hurry with magnum powders such as H110 / 296. I've had bullets jump the crimp and lock my revolver up with H110 / 296, just from not using an aggressive enough roll crimp. So I can say with certainty you would experience problems without a canelure to roll crimp into.
GS