Hey Michael,
Not sure if you've figured this out yet or not. If not, my recommendation is to put dev report suites in the account section of DTM and use the s_code editor to create logic that decides which report suite to send the data to. In my experience, the s.account variable in s_code overwrites the items defined in the Tool's Production/Staging Account/Suite.
I've also noticed that developers seem to get confused by (or simply forget to) remove the -staging.js in the <head> embed code for DTM. To get around this, I've started only giving developers the production embed code. I then use the s_code editor to send the data to the proper report suite (based on URL/domain).
Finally, you can use the DTM Switch Plugins to force the staging library in your staging environment for testing:
http://help-forums.adobe.com/content/adobeforums/en/marketing-cloud-forum/adobe-marketing-cloud.topi...
Hope that helps! I'm happy to entertain a discussion regarding doing things a different way :)
- Eric
