Excellent, that modifier will indeed solve the problem!

This is actually working relatively well. The shape keys intended for each mesh are importing correctly and it's only the ones intended for something else which are broken. The cloud of vertices is there to show you what couldn't be matched, which in this particular case is expected.

You should import the VTA file multiple times, once with each mesh selected. Then delete the vertex cloud object and go through each object trimming any shapes which are intended for a different part of the model. That will give you a correct import.

The importer really ought to have split the VTA file up in the same manner which it did the reference meshes, but I can see how that would be a total pain to calculate correctly.

Now please...don't send me any more meshes with shape keys called "VaginaOpen"!

Please upload the file you are trying to import.

Please upload the file you are trying to import. Are you importing it into a new blend file or an existing one?

Having messed around a bit I'm also leaning toward this being an engine bug, particurarly given the lack of any examples in Dota 2's content. The left-hand flex doesn't pick anything up even if I mess directly with the stereo split values. But if I turn stereo off then it's all right there.

If you're importing via QC then it may be that a flip command has been applied. There may also be animation which mirrors all the bones that you are now exporting as the reference position.

The second altered value is a rotation which wraps around at a number based on pi. The exporter's result is probably equivalent to the imported value.

Please upload one of the files you are trying to import.

You'll need to ask on the game's forums. If it shows up in HLMV then the exporter worked.

Looks like the API has changed. 2.80 isn't support right now, you'll just have to use the current release instead.

You need to set the up axis to Y before importing. It's fine then.