As a soldier you can volunteer to serve with gurkhas in R SIGNALS, RE, RLC, AGC and REME. Most posts will be specific to rank. Officers I suspect will have a wider ability to serve on attachment with the RGR depending on their current officer strength. R SIGNALS, RE and RLC officers can volunteer to serve with QGE, QOGLR and QG SIGNALS. Believe the RGR have usual AGC type posts (RAO and AGC Det Comd), and OC LAD. Believe some of their QM posts are also non gurkha - though I suspect this is likely to change post GTACOS.
They probably have an RMO and Dentist as well as other medical staff too.