Just bluetooth sniffing, what software does that, has to work on a Raspberry Pi
BlueZ is the official Bluetooth stack for Linux kernel-based family of operating systems. Its goal is to program an implementation of the Bluetooth wireless standards specifications for Linux.
It has command line tools of
btmgmt that provide the ability to scan for other devices within range.
To interact with BlueZ from a programming language then there is a set of APIs documented at:
There is an example in the source tree of using those APIs to scan for devices: