Much like how pilots and ARFF crews at PHX communicate with each other on 134.85, I have noticed that while watching videos VASAviation, pilots and ARFF crews at LAS also communicate with each other on the same frequency. What frequency is this?
In general, ARFF apparatus have AM aircraft radios in their rigs. They use them for airport clearances, etc. I'm assuming that at LAS, they can use either the tower or ground frequencies to talk direct to aircraft as needed. It appears that PHX actually has a dedicated frequency for incidents while LAS does not. It varies by airport.
Clink the Google link above which has a good explanation of protocol at LAS.