"The heat generated from these threads made me decide to leave sleeping dogs lie"

There is no reason not to add V3's grouping, too.
The DAZ EULA for V3 covers EVERYTHING about V3, and that includes her mapping style and the grouping.

Posette-V3 already IS a violation of DAZ' V3 EULA because the simple fact that she can use V3's textures already makes her a derivative work.
But DAZ doesn't mind, as long as she is only distributed properly encoded against V3.
In fact Posette-V3 has to be double encoded: Once against V3 because she uses her UV-pattern and secondly against Posette because she uses her geometry.

BTW, the V2 style mapping IS NOT covered by any EULA, that's why figures like Judy or NEAena or MAYA-doll don't need to be encoded against V2.

So regrouping Posette-V3 to accept V3 MAT's doesn't add any further legal problems.
As I said, Posette-V3 already IS a violation of DAZ EULA, so it simply doesn't matter if you add some more of V3's functionality.

DAZ is very generous in that regard: As long as you encode yourfinal  product using V3 as the key, you can "borrow" as much from V3 as you like.
But encoding IS a MUST.

And in Posette-V3's case, DOUBLE ENCODING is a must, because she also uses Posette's geometry.