Hi Curt,
what is the version of crystal you are using?
I am using Crystal reports 2011 and it is successfully send the main report and subreport data to excel.
Test export to your report to PDF format and test if you get sub report data or not?
Also check if you sub report contains "can grow" option or not, if you didn't check that option for sub report please check that option and test the issue.
Hope the above information will help you.
--Naga.