What sort of oscillator topology is used in WiFi/BT transmitters?
The carrier is generated by:

Cheap quartz crystal from 26 to 40 MHz and +/- 10 ppm frequency deviation

An internal PLL that pulls the frequency up.


There's no need for using a more precise TXCO with +/- 1 ppm frequency deviation because channels are pretty wide in frequency.
Harmonic filters are mandatory.

To answer your question:
The oscillator is a quartz crystal based CMOS oscillator.
The output is a square wave with a lot of harmonics.
The oscillator output is then brought to the input of the internal PLL.
The technological process is usually the well known RF CMOS.
Some, more expansive, integrated radio circuits are made in SiGe.