Do bolos for scouts have to be scout related?

That is a bit complicated.

The Boy Scout Uniform Inspection Sheet states, "the troop/team may vote to wear a neckerchief, bolo tie or no neck wear."

The Scout Leader Uniform Inspection Sheet says, "neckwear is optional but must be worn according to specifications in the insignia guide."

The BSA website (scouting.org) states that male Cub Scout leaders can wear a olive or tan dress tie, a leader bolo tie, or special adult leader neckerchiefs.

Th BSA insignia guide lists official neckerchief slides and describes several options for Boy Scout neckerchiefs. It says that the entire troop must agree and wear the same thing.

So it looks like a strict interpretation of the rules would suggest that the scouts can agree to wear a bolo, nothing or a neckerchief but all should wear the same thing. The leaders do not have to wear neck wear but if they do it should be a tie, the adult leader neckerchief (for Cub Scouts) or the agreed upon Troop neckerchief (for Boy Scouts). Cub Scout leaders for certain, and presumably Boy Scout leaders, can wear official bolos.

In actual practice adult leaders commonly wear scouting related bolos of different sorts, many of which are sold at Jamborees and other events. It is not common for Scouts to wear them, although according to the inspection sheets they could, especially if they all agree to wear one.