Bobc007,  The rule with using SAS and SATA drives is that you CAN mix both within the same controller. You CAN NOT mix SAS and SATA within the same Virtual Disks though. So the configuration you are looking for is a supported configuration. Let me know if this helps answer your questions.
I trying to put together a new server for our small business and wanted to know if I could use say 2 SAS hard drives in raid 1 configuration for hyper-v host (2012 r2) and then use 6 - 2Tb SATA drives in pass-through mode for use with storage spaces for 2 VMs. 
Mixing SAS and SATA hard drives in R730 with H730 controller