Thanks Mark -
We have a hack-y work around that does the job. Using the output dataset for Units, I created a simple 2 column, 1 row table that has the count of available units and the most recent updated date/time stamp, with a definition query that says only show anything when the available count is < 5. Using this as an input connector source in Geoevent, i just hooked it up to an email notification output in it's own, simple Geoevent service. It's basically an on/off switch with the definition query. Either it has a record, or it doesn't - if it does (indicating our condition is met), the email is sent.
This does the trick, but is pretty inelegant.
Allen