BM was under oath when he testified to the GJ. I'm pretty sure that his GJ testimony can (and will) be used during his trial testimony.
The relevant portion of Nevada's hearsay rules. BBM.
https://www.leg.state.nv.us/NRS/NRS-051.html
NRS 51.035  “Hearsay” defined.  “Hearsay” means a statement offered in evidence to prove the truth of the matter asserted
unless: 1.  The statement is one made by a witness while testifying at the trial or hearing;
2.  The declarant testifies at the trial or hearing and is subject to cross-examination concerning the statement, and the statement is:
(a) Inconsistent with the declarant’s testimony;
(b) Consistent with the declarant’s testimony and offered to rebut an express or implied charge against the declarant of recent fabrication or improper influence or motive;
(c) One of identification of a person made soon after perceiving the person; or
(d) A transcript of testimony given under oath at a trial or hearing or before a grand jury; or
Meaning, when you testify to something under oath at a trial or GJ that's not hearsay. And it can be used in court. The Claus Bros. will have a lot of fun with KM's & BM's GJ testimony.