I think to really answer this question AD and Pro.Umb, has to be thought of in the same post.
Well AD may bring a lot of followers from under some rockey stones, but I can't really understand Filch. The things Filch takes most pleasure in will deffently be illegal. That is the 'torture' of young children. Yes I said torture and thats what I think of his ways. But hey enough about that.
I think Filch is a very underground character in that he would 'align' himself to whom ever would allow him to receive his pleasures. This is obivous since other people have included Pro.Umb as 'the one he favours'.
The question thou, would he align himself to LV? I can't see any reason for the LV to use him, unless he is attacked by someone and needs a body. In an atempt to befriend Harry, or at least to learn his weakness, I'm sure he already knows that family and friends are very speical to him, since 'his real life' isn't that plesant (thats to say his life at PrivetD) But I can't see the real benifit of having him on the Dark Side, as of yet there is no evidence that he has any magical powers - maybe he was never trained?
To the main question, that being does Flich respect AD? Thats up in the air I think. I think it takes respect to work for a person, even if you don't like your boss. I guess you could say it is like Pro.Snape and LV, that is he liked what he was doing until it came to doing it, or finding out what LV was really like. (further more I think Snape is a very good character in that he WAS bad but now is GOOD)
So I think Flich is something that comes with the school, and I have a feeling that Flich was there even before AD, but I can't base that on anything.
I think that answers the main question, I lost my train of throught