Does PTC Arbortext Layout Developer 12.X have compatability with IPv6?

I don't think any such document exists. IPv6 is still such a niche thing that I doubt it is part of the design or testing of ALD.

I think ALD 12.x relies on Windows for all its networking needs, which are very few. ALD is a desktop tool that mainly relies on filesystem interactions for data load/save. There is a built-in debugger available via web browser but that tends to be used locally only. Also you could use Perl or Javascript extensions which may need network connectivity. I guess it would be interesting to learn the intended application for IPv6 with ALD.