I just flew a roundtrip between LAS and FAT today on Allegiant, and TSA-Pre was indeed available. I have entered my KTN number when I booked the ticket.

However, the issue is that Las Vegas McCarran International Airport does not have TSA Pre- for Concourse A/B but you can use the priority line, and get the semi-TSA-Pre experiences. I guess since most ULCCs still don't have TSA Pre-, LAS thinks that it is okay not to have it. The security agent told me that they had TSA Pre- for a while, but then took it away. I hope with Allegiant bringing TSA Pre- to the table, LAS will reopen the TSA Pre- lanes in Concourse A/B. I felt the TSA Pre becomes more useful when you fly ULCCs, which tend to have more first time flyers and occasional flyers, that take a longer time going through security.

Carfield