I've taken it on and off again in the past, and I did spend a little time trying to find out whether or not it was ototoxic, however I couldn't find much through Google. I came across one brand that had tinnitus listed as a possible side effect, and maybe a couple mentions on a forum or two, nothing overwhelmingly concrete though. I remember reading a few times that doxylamine might "mask" the symptoms of other ototoxic medications though.
When I was taking it on and off, I did find that it would reduce my tinnitus significantly while I was on it. However I thought I best err on the side of caution and stop taking it just in case because of the stuff I've read on other antihistamines like diphendramine, but yeah my research didn't really lead me to any real conclusions.