Neutral means you are allowed to hit that ball first. ACS rules say "the 8 ball is neutral on an open table" IE: the 8 may be hit first in a combination. I am not the one who determined the rules of the game in the OPs thread, the OP said his opponent told him he could not use they 8 in a carom because it was neutral. #1 players are allowed to use the 8 in a carom as long as they hit a legal ball first. #2 Neutral means that anybody may use the ball without penalty. Even if their particular bar rules say that you can not use the 8 in a carom he still called the 8 neutral. The 8 can not be neutral and an illegal (or foul) ball both at the same time. Please understand the reply that you are about to comment on and correct a person in before you reply.
I have never played where you can hit the 8 ball first even on an open table, but it looks like the BCA rules (which are a copy of the WPA rules) allow it. However, anything you pocket after that does not count so it's only really useful if you are playing safe. In either case, you can use the 8 ball in the middle of a combo or hit it in a carom at any time.
" Note: The table is always open immediately after the break shot. When the table is open it is legal to hit any solid or stripe or the 8-ball first in the process of pocketing the called stripe or solid. However, when the table is open and the 8 ball is the first ball contacted, no stripe or solid may be scored in favor of the shooter. The shooter loses his turn and any balls pocketed remain pocketed, and the incoming player addresses the balls with the table still open."