Yeah you can. I actually knew that from experiece too as I ran between 1 and 3 RAID arrays in my home computer pretty much from 2002 when RAID became common on motherboards to 2010 when I got an SSD. Once I got the SSD it really became unnecessary and I never even bothered setting up a RAID 1 with my data drives. I just back up to them individually. Sorry about that and good catch 4745454b.
You can RAID your SSDs and you will not even lose TRIM support. The latest Intel RST driver enables TRIM on the 7x series chipset boards but that's it so far. So I missed that one too.
It's actually a good idea to keep 20% free so TRIM / garbage collection will work correctly. Since an 120GB drive formats to 111GB that means 22GB free.