I haven't heard of this agency before, and I'm not aware of any specific communications information for them. In general, I would assume that it's a pretty tough target to nail down because they operate so infrequently.
A google search reveals this article, which implies that they are "part" of the SC Air National Guard:
South Carolina HART team performing challenging rescues
This facebook page would imply the same:
South Carolina Helicopter Aquatic Rescue Team
SC Air National Guard has a talkgroup assigned on the Palmetto 800 statewide network here:
Palmetto 800 Trunking System, Various, Multi-State - Scanner Frequencies. Given that they operate "state wide," one would assume they would depend on a statewide radio system to some extent. But I can say I've never heard talkgroup 27871 active in my particular area of the state, but I wouldn't think they'd be heard unless they have an operation in my local area.
If they have Palmetto 800 access, maybe they would achieve interop with other agencies that also use Palmetto 800 on the interop/mutual aid talkgroups listed on the Palmetto 800 page, including the SC Air-Ground and SC Air 1-3 talkgroups for air-to-ground communications that are used by other medical helicopter services. For communicating with local agencies that are not on Palmetto 800, it's anyone's guess what they might use. 155.340 is a good choice if they're working with EMS officials on the ground. Others of the interop frequencies listed here are possibilities, depending on what band the local agencies use:
South Carolina - SC Interop/Mutual Aid Scanner Frequencies and Radio Frequency Reference
I would also assume that their on-scene communications would be something "local", simplex most likely, and that they would use something provided by the ANG. I don't know anything about monitoring SCANG, but I would assume it would be in the military UHF range 380-420MHz. I'm not aware of any specific frequencies ever being identified.
Hopefully someone with more specific knowledge can offer up.