i could be wrong but i believe the terms are the same. hubcentric rings = hubcentric spacers.
your posts are a bit confusing. you are saying you have no spacers on the front and spacers on the rear? there are usually 2 reasons for using spacers. to set the wheel and tire combo closer to the outside edge of the fender for looks or to allow a rim that sits too close to the suspension or brake parts to be spaced away for clearance. did you order the proper offsets for your wheels? and did the shop suggest spacers from the beginning to allow a rim they have to fit your model of car?