I was also looking for a solution to this on reddit and I hacked together a solution that works. In the lensfun xml files I modified the Tamron entry for the 70-200 to this:
<!-- <model>Tamron SP 70-200mm F/2.8 Di VC USD G2</model> -->
<model lang="en">Tamron SP 70-200mm F/2.8 Di VC USD G2</model>
All it really does is comments out the old model name and replaces it with the lens id and then puts what I'm guessing is a display name as the name that actually shows up in darktable. But now the lens is being detected when I load a file in and the corrections are correct. Conveniently this lens requires pretty minimal correction, but I have a feeling that this will come in handy for other third party lenses that may not be detected correctly.