Afew years back, there seemed to be quite a few Zim pilots training in ZA; especially for commercial. Even the state sponsored CPLs were training near Jo'burg.
If they issue an ICAO compliant licence, it should be acceptable anywhere, as any other foreign licence.
If they've followed the South African model on type rating all aircraft, it may require a suitable endorsement on type.
It might be worth trying Irv Lee at Popham, as he can endorse ZA licences in the UK.