There were several V4 Xeon models that supported DDR3 AND DDR4 simultaneously. If you had a motherboard with an X79 chipset it would (sometimes) work properly.

I am not aware of any commercial vendor shipping v3/v4 boards with DDR3. I have a couple hundred Supermicro systems that are stuck on v2 CPUs with DDR3...

Get a 2696 v4 or 2686 v4 and a X79 motherboard and you should be able to use DDR3.