As
Whiskey3 pointed out, you may encounter simulcast distortion on the Tyler Simulcast site. The GRE/Whistler scanners are not noted for their performance dealing with simulcast. Of the scanners I use for monitoring the multiple systems here in the DFW area, most of which have simulcast sites, the TRX-1 does not do nearly as well as my SDS & x36HP scanners. My 325P2 is also better than the TRX-1.
While you may have issues on the Tyler Simulcast, there are two other Smith County TxWARN sites that should be in range,
Lindale and
Bullard. Neither of these are simulcast, and should be in range for you with a decent antenna. More than likely, you'd hear mostly county agencies, as well as those surrounding these two site, but you may not hear that much "Tyler specific" radio traffic on either one.
For your home county,
Henderson, the county's
system has four sites, but none are simulcast. Each site has its own set of frequencies.