Ena was the Thunderbirds' defensive coordinator and linebacker coach. He will be the Wildcats' new defensive coordinator.
Sitake was SUU's passing game coordinator and receivers coach. He is expected to have a similar role with the offense at Weber State, which hired Hill last week.
"I'm excited for those guys," Lamb said. "It's definitely an indication of the hard work they put in here. Jay Hill came after them hard and aggressive and with an attractive offer and I'm happy for them. I consider it a good thing for SUU a sign we're doing good things."
Clark and Ena have coached at Southern Utah for six years. Sitake, a former Thunderbird player, has been a full-time assistant for the last two seasons.
According to Lamb, Southern Utah secondary coach Demario Warren will replace Ena as the Thunderbirds' new defensive coordinator.
As far as a new offensive coordinator, Lamb said coaches currently on the staff will get the first look. The most likely candidates appear to be current co-offensive coordinators Teag Whiting and Justin Walterscheid, who worked closely together under Clark.
After Weber State fired Jody Sears after a 2-10 season, the Wildcats approached Lamb about its head coaching job.
He ended up signing a contract extension, however, which runs through 2020.
The Thunderbirds went 8-5 last season and qualified for the Football Championship Subdivision playoffs for the first time.