I've worked with TI BLE chips which were 8051 variants. Took me back to original CS classes as it is a very simple core with limited registers but can still be used to perform all the bluetooth functions.
IIRC, the BLE stack on those was a separate (undocumented?) core; the 8051 was for user software that gave high-level commands to the BLE block through magic registers. Still fun to program, for sure.