Does anyone know if it is possible to trigger the email send of a "recipients from results" saved search from a workflow? I need to perform other record actions before and after those get sent out, and I'd like to be able to automate it. The data attached would show rows from non-transaction child records, so email templates aren't really working either in this case.

What you are asking for is likely solved better a different way.

Would it be a consideration to have a process state field on the transaction to keep track of where the transactions are in the process. Then a workflow could process the transactions as the progress through the states. A drop down like “Ready for pre-send process”, “Ready to email to customer”, “Ready for post send processing”, “ Process complete”

It's not a transaction though. I think if it were I could script the lines. I am emailing the list of items associated to the vendor, and trying to track the processing status like you mentioned of that send and response, similar to what you mentioned, in a custom record. For those suggesting scripting, I'm assuming you mean you'd do it all from scratch?: loop through the vendors, get the items, build the HTML body, send the email plus do any tracking actions? Or do you know if the sending a search as "recipients from results" via script would work? I ask because I need to do this process for several different things, so the complexity is really blowing up if I code it all.

Code it all. Saved search emails are stupid flukey and Damn near impossible to know they didn't send unless someone knows it's coming and it doesn't come