Someone didn't know what they were talking about.
Good point. I have had two spas now with the Tri-X filters, and we have run them through the dishwasher with good results.
The one thing I found was that the one filter from the circ pump didn't come out white. I ended up having to soak that one and then run it again.
It's fine now, but I mention it because you may still have to soak and/or use some sort of filter cleaner if the filters get coated in oil. Once that was removed, the fitler came clean in the dishwasher and works fine. The dishwasher is the way to go with these filters because it gets back into the pleats in a way which would take a bit of time if done by hand.