The answer to this question depends on which Fresco Logic xHCI controller you have, which operating system you are using and which driver you are using.

Older Fresco Logic controllers FL1000 and FL1009 do not support UASP.

For FL1100, FL1100EX, FL1100SX and FL1100LX, UAS is supported by the controller but you also need to use a driver that supports UAS.

The Microsoft driver that is built into Windows versions 8 and newer (8.1, 10, etc) supports FL1100 and UAS so if you are using one of those versions of Windows then UAS is supported. 

For Windows 7 there is no Microsoft driver so you must install the Fresco driver and UAS is not supported.

 UAS is supported by the Mac drivers.