There are some really great plastics out there that in certain applications are a great choice.
Like the guys were saying, unless that OEM or other sleeve is in between the 2 nylon bushings, then there HAS to be some binding because your pulling the frame rails into the swinger rails when you tighten the swinger bolt.
The bolt gets torqued to the spec and thats it, I can't imagine that tightening it till it binds and then backing it off a hair is a good idea.
If you have the money, I'd go OEM. But, I wouldn't hesitate to give the nylon bushings a try if they do use a spacer.
It's similar to your front wheel bearings or rear carrier bearings, without that sleeve between the bearings, they are going to bind when the axle is tightened between the 2 bearings and collars.
The only other problem with plastics is stiction. Needle bearings are super smooth and there is no friction in a radial movement. Suspension is meant to be smooth and thats why needle bearings are used not to mention the rigidity of the setup.
I would not use them without the collar between them.
All our government does is distract us while they steal from us, misspend our tax $ and ruin our country