Unless I am missing something, no. I have 10.7 Server and it didn't download the 10.8.1 update.
When I tried to check for updates from a 10.8 client pointed to a 10.7 Server I get:
The operation couldn’t be completed. (NSURLErrorDomain error -1100.)
One of the things that has changed from Lion to Mountain Lion is the URL.
At home most of the macs are now 10.8 including my server, SWUDS gave the same error until I change the URL from.
http://myURL:8088/index-lion-snowleopard-leopard.merged-1.sucatalog
to
http://myURL:8088/index-mountainlion-lion-snowleopard.merged-1.sucatalog
Even the remaining 10.7 Mac couldn't get updates from the 10.8 server until I changed this URL.
Perhaps when 10.7.5 hits this will get fixed.