My SolusVM graphs have been showing 8Gb Swap usage even though the RAM is never over 50% used. Is it possible that virtual machines going into swap will reduce the IO of the SSD?
If you're swapping to the SSD, yes. Swap uses IOs; even SSDs, while not seek limited, still have IO limits. Granted, pageins/pageouts from SSDs are going to be very quick, so unless a VM is thrashing, it's not likely to affect IO that much. A thrashing vm might do more than 1k IOPs. Your SSD is probably rated for >30k IOPs. Then again, your SSD also has a finite write durability, so even under limits, it's not preferable to allow that.