Stellarium can interact with mounts in two ways, and for only two functionalities: send GoTo and receive current position. The first way is to establish a direct serial link with the mount, in which case it needs to have a file in the Telescope control plug-in that creates the connection and interacts with the mount. The second way is to use a standalone server that communicates with Stellarium with a simple protocol. In both cases, the code is C++, and a library giving access to MCMTII would be a good start. There is no INDI support in Stellarium.