I am not familiar with the specific county you have listed in your question, but generally speaking the DTMF tones are used to activate in-station and portable pagers that units use to be alerted to a new call. If they also use the long 2-tone QCII tones, the DTMF tones may only be used for a few specific pagers in use by that department, i.e most of their pagers use QCII, but they may have a few different units in use that use the DTMF instead. This would be the case if the DTMF tones are fairly rare compared to any other type of paging signal in use on their frequency. Hope this helps!
Actually in this particular case, the DTMF tones are used to activate local receivers which pass the paging tones to local VHF transmitters. This is a "temporary" setup until such time as all the first responders have UHF pagers.