My apologies, but what seem obvious to you may not seem so obvious to me
You indicate that you are using DragMath to place Mathml in Moodle resources. This would mean that your mathml is notinserted in the markup of the web resource, but on top of it, if you will. You then indicate that the code is not interpreted. Why do you think the code should be interpreted? That is to say, on what basis do you believe that MathML inserted via the editor (like so)
<math xmlns="http://www.w3.org/1998/Math/MathML"> a n ⋅ a m = a n + m
is interpreted by Moodle? Now, if proper MathML is made available to compliant browsers, those browsers can parse and display MathML, but that is not what you are doing....
To put it another way, if you wish to use DragMath then why are you converting to MathML, as opposed to exporting in ASCIIMathML format, or using the Moodle Latex format and then using MathJax?
I am at a bit of a loss as to what you are in fact trying to acomplish, in as much as you indicated that at least the obvious goal (having marth expressions displayed) is acomplsihed, aparently by way of inserting tex expressions with the core Tex filter or some surrogate in place.
So, perhaps if you could explain what your secondary goals ar it would be clearer, though if your secondary goal is to rovide a variety of ways to view the expressions, than I would have to say that MathJax, though not a complete Tek implementatin, does an extraordinary job, while ASCIIMathML is wonderfully easy tool to use as well.