Yes, omnisphere can stream samples, I even turned that feature off and let it load the whole sample, same thing...so yeah...I am definitely looking at getting an SSD in the near future to help with this.....
I am concerned though of the life of SSDs, they usually are only good for a year or two and then they start getting corrupted and bam...one has to buy a new one, unless someone else here has had longer life with their ssd's than what's been reported with them..