I get logged out a few seconds after I logged in to google plus video the popup when you click comments. I am then logged in to YouTube without the G+ intergration.
I use the self destruct cookie plugin, but it does not delete cookies that are in exceptions.
exceptions for cookies set are:
plus.google.com accounts.google.com apis.google.com youtube.com
It works as long as I keep a Google plus tab open, as soon as I close it YouTube will log me out of the comments and G+ notifications.