I have a couple thoughts here, none of which actually natively tie together the two result ids and send them combined in one email. That being said, here are some alternatives I can think of:
1) If the datasets are compatible, have a longer search that displays both sets of results. You can use the fillnull command to fill any whitespace in a table if it's bothering you that an entire column is null, for example.
2) Export both search results to csvs (outputlookup command) and pull those in as part of one search that sends an email of both contents combined (inputlookup command). This is similar to 1 but if the searches are hard to combine, this is likely a better option than an ugly join or append.
3) Assuming they have read access to whatever app the content will live in, you could save the scheduled searches to a dashboard and link the dashboard as part of the alert. I do that pretty often.
4) Write a custom alert action to pull in multiple data sources and does some custom action/js/html on it (this one is likely an add one to 1 or 2)
Personally, I like 3 if your consumers have the access/knowledge, because they can most easily play around with any results from Splunk than from an email. If not, 1 or 2 should get the job done if you can deal with likely empty overlapping information.
