for the entries stored on AD side, the compat tree creates entries on demand, and only when specific search filters are used (the same ones as posix-compliant systems would use) . You can find the list of supported search filters in RFC 2307 (
rfc2307#section-5.2).
This means for instance that in order to find the AD user
bob@ad.com on the compat tree, your search filter should look like
(&(objectClass=posixAccount)(uid=bob@ad.com))
Once this search filter has been used, the compat tree is populated and the entry can be found.
It implies that if you run id bob@ad.com, the compat tree will also be populated with the entry for bob@ad.com.
Hope this clarifies,
flo