It's not necessary to use a collar, and if the padeye is ahead of the headstay (eg on the anchor roller assy) as you mention - and that anchor roller is strong enough for the job - that's the cleanest way to run an A sail like a gennaker.
Some prefer not to use the collar because it prevents the tack from moving off the centerline and can reduce the projection of the sail... not using the collar may reduce the stability of the sail a bit....
Collar or not, the padeye/block forward of the headstay is probably best.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)