Quote by Swampy:
"Riding on the road helps you hold your line. Riding in a bunch helps you hold your line in a bunch."
Not so much...the most common shout on group road rides and in amateur racing is, "Hold your line!". Often followed with a descriptive adjective or a comment applying to family lineage. "Riding on rollers helps you ride better on rollers."
Most rollers are 16" wide. Subtracting a few inches for safety margin (again, 'most' rollers do don't have side bumpers), I think it can be assumed that rollers teach or at least reinforce riding precisely, accelerating precisely, riding with no hands precisely, changing hand positions precisely, pedaling efficiently and precisely, correcting rider position errors on the bike to enable precise riding and they promote a relaxed yet deliberate concentration that translates well to the road. They build confidence.
Will riding rollers make you a crit god? No, but it sure isn't going to hurt any.