on nfsserver.mydom.com there is a user entry in /etc/passwd that looks like this:
In this case the user has no access to login to the actual nfs server but the user and uid does exist and is matched from the nfs server and client. Quotas still apply.
I do no know what the setup is on the OP's network -- nor what the "Linux and Solaris don't talk" junk is about. What I would do is set up a cron on the nfs servers that runs a perl script that gets the output from repquota or vxrepquota and parses it then inserts it into a db server somewhere. The web app can then query the database and pull out the usage and quota info for the nfs server that is needed -- with no root level exposure to the nfs server.