A simulcast system is one where all sties transmit the same information in sync, at the same time. Each site is a clone of the others. So, for example, if it is a 10 channel system, with 5 sites spaced about the county, they will all have the same channel 1 frequency, same channel 2 freq, same control freq, etc... The data on the control channel and voice channels is exactly the same, and on the same frequency, at every site. They use GPS for timing to keep everything synced up.
So, you can consider a simulcast system exactly like one large single site. There is no need whatsoever to program each site of a simulcasted group of sites as its own site. Just lump them all together as one larger site and pick a location somewhere in the center of the coverage area for the latitude and longitude, and set the range accordingly.
You can tell if a system is simulcast by looking at the FCC transmitter frequency allocations for each of the sites in question... if they are all licensed for the same group of frequencies, and all those sites overlap just a little, then it is most likely a simulcast system.
It would definitely work better if each site could have its own group of channels, but there are sometimes not enough frequencies available.
Simulcast is next best option, but its not as good because there can be areas where the signals overlap and cause destructive phase cancellation. Motorola and Ma/Com have complicated algorithms in their receivers to combat this problem but don't expect a scanner to perform as well in some of those areas. Especially in digital modes.
One more note: Most wide area networks, like Palmetto, or VIPER 21 are a conglomeration of county-wide simulcast systems. There might be 59 sites listed in the RR database, but each so called "site" is really a group of a few closely spaced simulcasted transmitter locations all operating on the same frequencies to improve coverage. Or it could be just one transmitter location, if the coverage is sufficient. But either way, to program these in, you set up each "site" as listed in the RR database, as if it was its own single site.
To sum up: "Site" in RR refers to a Uniden zone, not "transmitter tower site." And an "RR site" might be one transmitter or a bunch of transmitters grouped together. But either way, you consider an "RR site" as a single site in the UASD software, regardless of how many transmitter locations, and you will be good to go.