I'm still running Lion Server 10.7.4 with ML 10.8.2 clients with no problem… mobile home sync included.
There are a couple of caveats that springs to mind to that which might be bothersome to you. For the life of me I can't get Notes to work from my Lion Server. So if any of your clients want to use server based Notes then you might have to go with some other solution. As everyone also has an iCloud account I've enabled it on iCloud instead. Slower, and I shouldn't have to do this, but works.
SSL in Mail always wants to be on for SMTP, even though there's a checkbox to turn it off, so if you're not running an SSL certificate on your Lion Server you might have issues here as well.
I recently upgraded a 10.6.8 client to 10.8.2 and everything works great on network, but the mobile piece is not letting him login at home. Suggestions? Used to login to his mobile managed account with no issues off network.
Did he maybe not complete a sync before he left? Shouldn't user credentials still login him to the machine?
Server is 10.7.4
Irrespective of the state of sync, one should still be able to login to an account. The only way I can see a sync causing problem is if the account was logged into as a network home account and the more recent changes got copied over sort of half way through. Even still, that shouldn't prevent a login rather there may be some account "weirdness".
The first thing I'd check is whether standard user accounts login correctly when out of the local network to be sure it's not a system issue. If standard accounts work fine, you might want to remove the account from the system and then re-add it.
If you have another network account user using 10.8.2 that has no problems running outside the local network you might want to try their account on the system to see if you have no issues with it. Otherwise, just create a new account to play with on the system and see if that works ok.
Without know where it's actually stalling it's sort of hard to say what to do but I would try to identify whether it's a system problem or an account problem first.