I have one 2070 Super with 8GB of vram.
Thinking about putting a second one in and connecting them via nvlink.

Does anybody know or have experience with benefits to the opencl parts of pyro, flip, whitewater, etc. and if those even recognize a nvlinked dual GPU setup?

NVLink support has to be added by developers, for example like Redshift and Chaos Group have done for their renderers. OpenCL in Houdini will only use one GPU, and moreover I'm not even sure OpenCL in general works with NVLink.

thanks for clearing that up!
I think the better route for me is to probably go with a threadripper for simulations then.

I would say so. The trouble with GPU OpenCL is that you run out of VRAM pretty quick when you scale up sims to a decent quality.