Can a LEED project use exhausted/waste heat (and claim credit of some kind) from an adjacent building that is not being included in LEED project boundary?
In some instances land and facilities outside of the LEED project boundary can be used for compliance with specific credits. Examples include EBOM's SS Cr #5, stormwater calcs, shower facilites outside of the LEED boundary to comply with SS Cr #4.2 etc..
In your case the LEED plan reviewer may require a detailed narrative of the waste heat, when it is available, how it is supplied to your LEED building,etc...
My suggestion is to submit it in the design phase with a detailed narrative. If the reviewer does not allow credit for this strategy simply remove it from the energy model.