While coffee grounds are an organic source of N, it's at a pretty low level - far lower that you would find with a standard azalea fertilizer. Even organic Hollytone tests out at 4-3-4 - coffee grounds at 2-0.3-0.3. And dry fertilizers from organic sources are not effectively utilized in a container planting situation so you may not even be getting the full effect of the UCG's in the first place.

I doubt that it is elevated N that is causing the lack of bloom and lackluster growth but perhaps just an all around nutrient deficiency. How long have these plants been in a container? Did you start with an acid based planting mix and has it been refreshed at all? And how do you fertilize them? ALL plants grown in a container will need routine fertilization - depending on product, once a growing season at the very least. The nutrient content of any potting mix is negligible and the plants rely on the grower to provide what they need. An all purpose liquid fertilizer with trace elements is generally considered best for this purpose.