You have the proverbial nail right on the head.
The only reason that this does not work is lack of support within Digi's SNMP MIBs.
For anyone who desire/need such a feature I encourage you to contact your Digi sales representative or support and make an official request for it.
I should clarify my original statement a bit, however. When I said that it was not supported I meant in respects to our Connect Integration Kit. If you are a development kit customer this is certainly possible, by the creation of your own MIBs.