Can SAS drives be used with SATA controllers?

From Wikipedia:

SAS offers backwards-compatibility with second-generation SATA drives. SATA 3 Gbit/s drives may be connected to SAS backplanes, but SAS drives may not be connected to SATA backplanes.

The SAS protocol supports tunneling SATA commands over it. Thus, a SAS controller can communicate with SATA drives or SAS drives. However, it doesn't go the other way. SATA controllers can only communicate with SATA devices.

Supporting mixed drive types is a vendor-by-vendor, device-by-device thing. Generally, this is not well supported and will cause both drives to run at the speed of the slowest drive. Support will likely improve in the future.