I would highly recommend AGAINST this. I have been using Time Machine over my home network to a volume on an iMac server and it works great - until I tried accessing it from work via BTTM. First, Time Machine seems to have a tremendous amount of network traffic in both directions so everything is very very slow (T1 at work and Cable Modem at home). But more importantly I has some network disruptions and I found the backup volume was then corrupted. I had to through it away and start over. Not a total disaster but very very inconvenient.
So, in principle it does work but I consider it highly risky.
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So, in principle it does work but I consider it highly risky.