R&S equipment is pretty common in the cellular industry. There is more of it out there than you would think. While this particular signal generator is maybe not the most common piece of equipment you will see lots of R&S spectrum analyzers and the like.
It's technically not a signal generator but an Arbitrary Waveform Generator. It provides a base-band modulated signal to the signal generator which the sig gen upconverts to the RF carrier. If you purchased a Vector Signal Generator this would be built in but you can still buy them stand alone and they are pretty common. NI, R&S, Tek, and Keysight all have product lines of them.
Another way to think about it, this would be comparable to a signal generator in the same way that an oscilloscope is comparable to a spectrum analyzer.
What you call a signal generator is what most would call an RF signal generator. Both an AWG and an RF signal generator belong to the generic signal generator family. :-)
There are probably only a few electrical engineers in the entire world that actually use this stuff on a day to day basis.