I have read of some leaving the pin out to help the barrel "float" better and possibly increase accuracy. I have also read of some who say it is necessary to fix the barrel firmly for better accuracy. I personally wouldn't leave any factory part out of any firearm that I was going to shoot.
Are you referring to the slide stop, or the supplemental pin that goes beside the slide stop and is not present in centerfire 1911s? This part?
If the latter, that part isn't used in Kimber Rimfires and conversions or in Ciener conversions. You're safe to shoot without it and you probably won't ever miss it. You'll still have the supplemental screw, and the Kimbers and Cieners don't even use that.
I'd recommend you check out www.cwaccessories.com and look at the kit they have to do away with the pin (screw) on the right side of the frame that screws in...as well as their Performance Enhancement Kit. I upgraded my GSG1911-22 with these parts and the gun is much much more accurate now. You still need that pin on the left side that goes in and is held in plce by the slide stop. Leaving the pin out is not going to help acuracy at all. It is a FIXED barrel pistol. It might even be somewhat hazardous so I wouldn't leave any parts out when puting a pistol back together...this ain't no BBQ Grill you got from Home Depot now.