Finally got around to reading http://www.uesp.net/wiki/Lore:The_Horror_of_Castle_Xyr today and notice "b'vek" was used. Is that a way of saying something like "By Vivec?"

Anyways, that's what it sounds like to me, let me know what you think....

I think you're right--either "by Vivec" or just a very lazy contraction of Vivec.

Yep, B'Vehk is a casual way of invoking that floating chap.