Under the admin settings for the directory server (/admin/settings-directorygroup.jspa) you should be able to define an "Area Filter" that will only pull groups in those two areas.
Something like |((cn=ResponsibilityDomain)(cn=forums))
You will probably have to play around with the filter from the command line to make sure it is pulling what you expect for the groups. If the field containing the membership is called "uniqueNames" then combine that with the query like this: &(objectclass=uniqueNames)(|(cn=ResponsibilityDomain)(cn=forums)))
So yes it should be supported if you can get the filter setup to match and it looks like you can.