No, it wouldn't matter what languages the two systems are built in. Communication between disparate systems is achieved when each supports standards, and/or when one provides an API which any external system can use.
You start with figuring out what is possible for Moodle in terms of being able to log in from a disparate system. Then figure out how to do it from DNN or whatever other app folks have logged into. Would you store the user's Moodle credentials in a DNN table and pass them securely to some Moodle login API? OK, probably not too hard to figure out. What happens when the user changes her password in Moodle? You need to handle the login failure in such a way that assists the user to update those stored credentials and then login successfully, with as few calls to the help desk as possible.
Another possible approach is to have each application use the same authentication system, such as authenticate against AD and use Integrated Windows Authentication. Then you don't need to communicate between the two. That works best as single sign-on when students are on-site and logged on to the network, and would probably still require two sign-ons, though the same credentials would be used each time.
There is, I believe, a SCORM-based Course Management System built in DNN. Do some searches in these forums - the Announcement forum, maybe. If you're not committed to Moodle, that might be a consideration.
There are (read: expensive) identity management solutions which can do all of this in a much less messy way. Oracle Internet Directory / Identity Managment is one. Microsoft has an Identity management interface as well. These are solutions for larger institutions with many disparate systems, when integration of such systems is difficult or undesirable. They perform true single sign-on capacity with password and account management from a single location for various applications. Not the first stop on the effort to integrate two systems, but worth knowing about.