We biked for about 10 years.
Always stayed on Blue. Sometimes they wanted to see tickets, sometimes they didn't.
As far as I'm aware, there is no secure parking for bikes anywhere at Le Mans - it's not a HOG Rally!. I would suspect, as stated previously, you're better off parking the bikes on a camp site.
It's interesting to note that it's impossible to securely retain a pass on a bike.
You could load your kit from the bike into a car and then ride onto the site, without any kit on board the bike, as though you were returning from a local ride and claim the pass has been nicked form the bike.
Unethical, I know. But it works.