Marketing to Youtube Subscribers...Is this possible?

I dont know of anyway to mass contact their subscriber list, but you can certainly get on Youtube and build up your own subscriber list tho.

A lot of the big YouTube players are doing cross promotions; involving shooting a video with each other. Other times, each YouTube user creates a video for their channel but it's promoting the other's channel and videos. I don't know if you have a large number of subscribers but most users won't collaborate with you unless:
A. The number of subscribers is close to theirs, or at least beneficial to them
and/or
B. The content is related to the content they are creating.
There are techniques to get other YouTube creators to work with you, one technique is to do them a favor; such as create a video that promotes their site. You really have to focus on helping their business before they will help yours.
Other things you can do is create video responses to their videos. Comments can help too. However, there isn't any way to send a mass message (like email) to all of the subscribers on their list. Subscribers do get notified in their email that a new video has been posted, that's why you want to partner and create a video with the user.

I thought you could use a program like tubetoolbox to extract the subscriber of a channel and then share a video with them that directs people to your squeeze page. Isnt that tubetoolbox 101. Find channels that are like yours and leverage the subscribers/viewers of that channel.

Very possible! Whenever you have a video, subscribers get notified. Always make sure you have a link to whatever it is you're offering or a link to your blog. At every video, give a strong call to action in the end. Direct people where to go and what to do.