There are messengers who road race here and do quite well at it. I know several who have made it to the senior 1 level of road racing. A few of these guys win races on a regular basis. So if you take 1 guy from the senior 1 field who has never messed...and one of the senior 1 guys who works as a messer...I think its safe to say the messer guy wins hands down. Familiarity/comfort counts a whole lot. Guys who road race get comfortable with closed courses and a pack who for the most part know the rules/etiquette of road racing. What are the rules/etiquette of an alleycat race? Prolly just that the guy you cut off is waiting at the after party for you to show up. Being fast is good. Knowing how to ride in traffic and knowledge of the city is good. The best balance of the 2 will win alleycats every time.
For the record you can have your racing license taken away from you for doing non-sanctioned events. Many guys dont do alleycats for this reason.
At the H.P.R. in Vancouver a few years back a couple of guys from the Canadian National Track team showed up to try their legs out on the figure 8. I was doing staging for practice at the time. Both these guys were waiting for their turn to do some practice laps and looked really nervous. I asked them why they were so sketched out seeing as they have had more track experience than any one else there. The answer? "We never turn right!" 2 national class track riders bowed out in the first round of qualifying because of this simple fact.