Interesting question! It is supported to use drives from different shelves in the same aggregate and/or raid group. If HWU says the drive is supported in the shelf, then that is fine.
Mixing of drive technologies is not recommended, but different speed interfaces on the same drive technology should be fine. In either case, the drive will be slower than the maximum speed of the drive interfaces, and the backend connection from the shelf will still be 4x12Gbps.
For final answer, you should contact the partner solutions centre for your region. Please feel free to provide me your corporate contact details and I will connect you, or you can find the document on fieldportal outlining the partner solutions centers.