Will institutions allow credits from your JST to be applied to your efforts to earn a master's degree?

My captains career course counted for 6 graduate credits because Army Sustainment University got several courses externally evaluated. Usually the answer is no, up to the university granting the credit

It is possible, but not likely in most cases. Just like the undergrad degree, it will depend on the institution, but for most Army courses and experience (most, not all - things like ILE or CGSC may be exceptions), you will have a very hard time demonstrating that these things reach the level of experience/ learning / critical thought / technical application that a typical post-grad course requires.

Unfortunately I agree with most of the comments here. Working for a university, (Purdue Global) we do review all JSTs and actually do award credit for major requirements (not just gen eds) for under grad degrees. We’re currently reviewing the Sergeant Major Academy course for any articulation into our MS in Management but in most cases, it’s unlikely to get much credit for a grad degree, unless the degree is built specifically around military training.