It has been a few weeks since my last gold medal on my local server, and I just got another medal today. I haven't even tried to turn VAC off of my local server because I don't think it's needed. Just put -insecure in the command line parameter for safety.
As long as you do this on a local server (friends-only server), just for survival, or go to single-player and do off-line campaign, I think the trainer won't cause VAC to flag your Steam account for cheating.
Just remember: Don't play with this online and don't play with other online friends.