Most ear seals for headsets are foam filled. The gel versions are filled with silicone. They are more pliable than foam and will conform to your head better thereby getting a better seal. It also spreads the pressure more evenly making them more comfortable.
One of the urban myths I heard about gel seals started when I was a pilot. David Clark is the preeminent headset manufacturer in the aviation world. Myth is: when the FDA banned silicone implants, David Clark bought a tanker car of the stuff real cheap and started making headset seals from that purchase. Don't know if it's true, but makes a good story. (BTW, if you think noise canceling is expensive for shooting, try a set of David Clarks for flying - mine where around $700 - nothing in aviation is inexpensive).
Don't know if they're available for the Dillons. Call and ask, if enough people do, they might make them.