Using Exact Target it is very possible to track conversions, using a basic img tag which passes some xml to the tracker.

You can read about how/what is required here: http://help.exacttarget.com/en/documentation/exacttarget/content/conversion_tracking/

Making this work with Google Tag manager is a bit tricky, but very possible

The process can be done in 3 easy steps:

1. Capture the relevant passed params from any cliked url

2. Pass that data to teh datalayer

3. Use the data in GTM