I think nsvhr does it's own virtual hosting. The VAT module uses one AOLserver instance to serve multiple domains. The VAT module runs as a filter similar to the OACS request processor but runs before any other filter. The VAT module compares the value of the Host header with its in memory database (nsv arrays). If there is a match VAT starts looking for static files in the configured location, then template files, then returns filter_ok if it doesn't find any files. If there isn't a match it simply returns filter_ok. If you have OACS installed, that means the request will the be picked up by the request processor. VAT doesn't work with or know about the OACS subsite module.
If you load the VAT module, and don't configure any domains, it should have no effect on how any request is served.
