Our nursery and property are open to the deer. They come through 1-5 at a time. Here is what they do in our nursery. If you plant heather on their daily trail, they will trample it to death. If you plant it next to their trail they may take a passing nibble of little consequence. If it is out where they don't usually go, they ignore it for the most part.
Here are the exceptions: They can seek out and nibble back Erica vagans. It does still bloom but with shorter stems. They often "prune" when it is in flower. If we could just teach them when to prune. . . .
Our tree heath Erica arborea 'Estrella Gold' is 5 years old and should be 4 feet high. It is 4" high. It is planted near an apple tree where they hang out and defoliate the branches. All the other tree heaths are only occasionally nibbled a shoot here and there. It is not even noticeable.
They eat Daboecia flowers once in awhile. A Daboecia can be in full bloom one day and half bloom the next. Fortunately, Daboecias are good at flowering again shortly after pruning.
Some winters they can prune back the Erica carnea in certain areas that they like to hang out in. New plantings can be pulled out from taste testing. It is a good idea to regularly patrol new plants to find ones that have been pulled out of the ground.
Heather is, for the most part, deer-proof. They have never killed a heather from browsing, just from trampling. This can be avoided by not placing plants on their trails.
It is worth noting that most deer in most settings across the country never touch heather.