axebeak

> NPointGroups 1 NPrimGroups 1

You have some groups declared in the header, but apparently there are none in the geo's body.
Set the numbers to 0: “NPointGroups 0 NPrimGroups 0”.
For some reason GPlay is more forgiving about this and can parse such ill-formatted files.

The new geo format is different indeed, it's JSON-based, to save out an old-style reference file select .hclassic in the format drop-down.

Attributes can be added in VOP with Bind Export, but in this case it seems more convenient to use Vertex SOP to assign UVs:
u = vector4(0,0,1,1)
v = vector4(0,1,1,0)

You can use Intersect inside VOP COP generator to cast rays manually and then sample attributes at hit positions using PrimAttrib (it'll return interpolated values for point attrs). It's slow though, but sometimes can still be useful.
I'm attaching a simple scene to demonstrates this.