Since no one else will jump in and guess, I will offer that it may be some kind of spurge (Euphorbia spp.) - looks very similar to a couple of species. Clear close-ups of the flowers would be helpful. One trait is that Euphorbia species usually bleed white, somewhat toxic sap instantly when the stem is broken.
I have no idea how it might affect plumeria.
hortster

Thanks! I looked online and came across spurge, but it said it was low-growing, so I thought maybe not. But maybe so. :-) I'd love to get a close-up of those flowers, but they're pretty much microscopic, and I was having trouble keeping both the plant and the camera still at the same time.

There are more than 2000 species of spurge. Growth habit may also be influenced by shade. so a plant that is normally prostrate could grow erect in different circumstances.