Bill- apparently xanthomas are fatty deposits can be in many locations, including tendons, in hypercholesterolemic people. There are several articles about this out there but I don't know what the prevalence or relevance is... See this one if you're up to a dry read.
The way I read it, fatty deposits within what shold be more solid connective tissue(tendon) can't be a good thing, and if the deposits are on the surface of the tendon( as palpable nodules) that can't be good for the interaction between it and the paratendon(sheath). But take any of this as FWIW...