Did the pheromones idea come from Enterprise? It's not something I remember from any other source.
I actually like the idea of pheromones if it's something voluntary
, which is something a sexually-advanced species like the Deltans should be able to do. It makes sense, if they have sensory and extra-sensory powers related to that aspect of life, for them to have refined biochemical control too; Deltan courting could be a delicate dance of chemical cues in addition to its other elements, with the right cues needed to make sex possible at all. (I know the original idea was for Deltan foreplay to consist of "lovers putting images in each others' minds," but how boring is that...)
I like the Deltans much too much, admittedly. They're my favorite under-used Trek species. If I got to write them for a show I suspect I'd be one of those writers giving his pet species new super-powers every other episode...
(As for Oath of Celibacy business: maybe we should take it with a grain of salt? If the Deltans observe it as strictly as humans observe the Prime Directive...)