>> How often do they have radio traffic on local PD frequencies?
That's kind of like asking how cold does it get in Colorado. You say "not very cold," but I freeze my backside off if we fly out to visit the wife's family in Estes Park.
Bottom line for Myrtle Beach / Horry County is that the law enforcement communications peaks with good weather days, and events that bring in alot of tourism.
Most all of the public safety communications takes place on 800 MHz trunking systems, Brandon. You mentioned recently on another thread that you currently didn't have a "digital" scanner, and I didn't see a trunktracker among the equipment in your hobby room photos. Although digital won't be necessary, a trunktracker will be to enjoy public safety communications in Myrtle Beach.
I really can't comment about amateur radio activity in the Myrtle Beach area, but you might want to check out the Grand Strand Amateur Radio Club.
There are also some RR members from the Myrtle Beach area who might comment on this thread.
Have a safe trip, and enjoy ... but leave the snow behind in Colorado.