The Reliant studio model clearly had the same retractable doors on the saucer's underbelly as the Enterprise had in TMP. In TMP,those Enterprise doors were displayed open revealing very similar, round, airlock doors, though I don't think they were built on set as full fledged docking rings for travel pods. They looked more akin to how the airlock doors appear from the interior, probably as a cost saving measure by reusing other set elements. However, I don't know how the scale miniature depicted them, and the scenes with the on set version were never seen fully completed, despite being seen in some extended versions of the film. You could easily make that call yourself.
I think those are more like EVA hatches for men in space suites. They were used as such in TMP. The doors on those hatches were almost flush with the back wall of the alcoves they are set in, so you are right, they can't mate with the docking ring on travel pods.