It would depend on what was meant by 'supplement'. The problem with videos is, like books, some folks think what they see 'must be right' because it was published. This can be difficult to resolve when what they see is not what they are taught in the dojo.
If they want to learn perhaps new ways to do techniques, recognizing that it may not be what Sensei wants to see on the mat, then most of the 'big' names you can find via Bujin and the Aiki Journal are great.
Or if you happen to belong to an organization who follows one of those 'big names' then by all means get one of those if 'supplement' means practice more on your own. I made this recommendation to my last dojo, where more than one style of weapons was taught: mostly style 'A', but the test by the 'visiting pro senseis' was going to be style 'B'.
If they don't follow a 'big name' (or even if they do) and want primarily to be sure they are doing what sensei wants to see on the mat, then 'informal' videos of him teaching at seminars/other classes, and seniors taking tests, are to my way of thinking the best. They are not as glossy, and no special slow motion explanations, but they show you your sensei and /or sempai doing the techniques, which is as close as you get to private lessons without being there.
Sometimes I wonder about some of the 'big names' with videos out, made by some many years before...if Aikido evolves (and it did for O Sensei, so please no new 'tradition' arguements), then I wonder what those instructors now think of what they have on tape, and if they ever wish their students would stop copying it so exactly. Is it like looking at old high school yearbook pics for us? I train sometimes at a dojo belonging to a 'big name' organization, one of the senseis who in his talks stresses innovation and evolution of the art. And his videos are treated like the 10 Commandments----there will be no way other than this way. I can't help wondering if he would really want it that way.