In a league setting, 1 urethane ball may create some carry down. 4 or 5 guys throwing reactive will chew up the pattern, much more and faster.
I would think main way that urethane will mess up your bowling, is if you think it is, or blame poor shots on it. If you go in thinking this guy is messing up your shot - you probably messed up your shot b/f he throws a ball down the lane.
That being said - probably a solid reactive ball would work better, just whatever you have that rolls a little earlier. If there really is carry down, you need to get around it by going a little further inside and getting your ball outside of his line. Realistically, you may just notice the shot breaking down a little less than usual.
Some other things that effect carry down besides just urethane are rev rate and what "urethane" ball is being used.
If he doesn't have much hand - well anyone with a lower rev rate will alter pattern much slower.
Also, what ball? A black hammer that isn't going to flare or a Fever Pitch that will?
This summer I used almost only "urethane" in two sport shot leagues. Thankfully, no one seemed to notice, care, nor complain about me messing up the shot.