Well DeaC, you may have been right! After setting out the beer and pellets for 2 nights I didn't see any slugs or snails (or any traces of them), but I certainly noticed an influx of cockroaches. They were having themselves a wild party with the beer I provided.
These nasty buggers had the nerve to hide inside the vanda vase when I turned the porch lights on
I don't have definitive proof that the roaches were the ones nibbling the roots, but a little bit of research suggests they like to eat orchid root tips as well as flower buds.
I went and sprayed the perimeter with spectracide, so maybe that will finally solve my issue.