This is not a problem although we wouldn’t recommend it on a regular basis. The UltraStream was not made to put hot water through it. However…
When hot water runs through the filtration media in a cheaper filter it creates tunnels. When tunnels are created the water can run through without contact with the media which means it doesn’t get filtered anymore.
We designed the UltraStream to make sure that hot water wasn’t able to tunnel. We use a  specially designed ‘spreader’ that forces the water to spread evenly which means that these tunnels just can’t happen. The negative side of any hot water intrusion is that hot water will ‘liberate’ some chlorine already accumulated so you’ll get high chlorine output while the hot water is passing through.