It's true - in FAR 6.302-3(b)(3), "Expert Services" refer to what can rightly be called "expert testimony", or the use of expert to assist the Government in evaluating or defending against a claim. So when you use this to validate the sourcing to an SME in logistics to perform under a prime contract, DCMA is going to look askance at your justification and likely beat it within an inch of its short life.
So how should you handle SMEs that you get through "unofficial direction" from COTRs or PMs? As I've said in earlier posts - specialized staffing companies!