Summary Count in Text-Multiple Choices Field

Yes you can do this.  

First make a summary report  and in the "summarize" section select those two fields.

The further down the panel. Create two "Step 1" Summary Variables for those two same fields. 

Then Create a "Step 2" summary formula. Be sure to set the field type to be formula numeric percent and set your decimals (probably set to 0 decimals). Then I suggest saving the report and opening it right back up again to customize.  That way the report will know the name you gave for that percentage calculation.  Then add your summary formula field  for the percentage to the same section where you chose those first two fields for your report.