This technote,
http://support.veritas.com/docs/273123, points out that EV does not archive disabled AD accounts but it also mentions another technote for using EVPM to set the 0 day policy and then do a Run Now, so it may be that scheduled archiving doesn't work, but a Run Now does.
You could verify this by setting up DTRACE (
http://support.veritas.com/docs/276120) and as you have EV7 you can do the Admin Console option, select the Exchange Archiving trace (name may not be right - doing this from memory) then do a Scheduled run and a Run Now - the trace should show why the disabled users are not being archived......if in doubt log a case with support:)
Thx,
Mark