Huh - I wrote a question like this years ago. Cheap RAID SSD. You won't get anything like the performance of an SSD from this, probably less than the performance of a decent HDD. The best, class 10, SDHC is class 10 because it gives a sustained IO rate of at least 10 MB/sec. It would take an awful lot of those to add up to a decent HDD.
Motherboards will not RAID USB drives. Generally, they rely on the southbridge which can only RAID SATA drives attached directly to southbridge ports, or a Marvell chip that can link two drives in a strange proprietary implementation of RAID 1 or RAID 0.
Short answer: no.