I feel very unsure about u-verbs, and treat them as a-verbs, but that is not really an answer to your question. I at the same time see no reason why my feelings should be either right or wrong. 

I think the inceptiveness (is that a word?) of -u verbs is a wonderfully useful concept, but I will need a few more re-reads of the relevant essay(s) to be reasonably certain of the structure and any controversies (in some of the QVS essays the -u verbs seem just simple verbs).
How the concept would manifest, if at all, in Sindarin, I have no idea at the moment.

Interesting, that in Gnomish, EQ kelu had the cognate celu, but EQ lutu appeared as lud.