The proof, as they say, is in the pudding:
I did this multiple times in this post, in fact the "4" with the upvote is another one I just did in the post, but I had forgotten to take a screenshot before I did it. I also made a view upvotes for other comments in this post today (even though it's been deleted for a while).
It's important to note that I can seem upvote comments for other deleted answers (that are on deleted questions), but not the comments on the questions.
To reproduce that it actually 'took', I also cleared my cache and opened it on another browser.