[posborne]

Very often. Vendors such as NXP/Freescale, TI, Intel (and Chinese manufacturers on top of MIPS) all tend to target Linux-first. For some drivers (e.g. wireless), you sometimes need to work directly with that vendor (Qualcomm/Broadcom/...). In my experience, it is almost the default except in cases where you need 1) Hard real-time, 2) Very low power (most battery applications), 3) Very low cost. Those still go to MCUs where life is more difficult for anything complex (e.g. requiring graphics, a network stack).

For most embedded use cases, Android is still not suitable as you have to jump through many hoops to get sufficient control over exactly how the device operates (you can make it work but the further away your device is from a phone/tablet, the harder it gets).

Source: Worked in embedded design services until recently.