I actually found the answer. It works similar to crossfire/sli, in other words, when rendering, it maxes out at 16GB which is not that surprising considering that the last professional card with 32GB was the FirePro W9100 and since the "Radeon Pro WX9100" hasn't been released yet (I'm assuming that they're are gonna make a new FirePro W9100 since the Radeon Pro WX series is the new line of professional cards.), I think it's pretty safe to assume that it'll come later, hopefully with vega architecture (AMD please!).
It's a somewhere in the middle.
Alas, it is a bit disappointing (I wanted 32GB of vram lol) but still hyped for Vega!
This is a german page. And you can translate the sentence: "Der Speicherausbau beträgt 32 GByte, wenngleich sich die 16 GByte pro GPU nicht addieren."
It means, that you have 16 Gbyte per card, but you can NOT summate and use full 32 Gbyte for textures. It's like having crossfire, how you explained above. Effectively you will have 16 Gbyte.