There is a way (at least for blogs and polls).
For blogs :
- You go in the admin console under "Autorisation --> Auroisaton relative to blogs"
- You edit the permissions for "Everybody" so they can only read and comment personnal and system blogs.
- If you need to, you create another security group for those who can post in personnal or system blogs.
For polls, you can put this system property that will remove the possibility to create polls in a user container : jive.usercontainer.poll.enabled = false
I'm not sure if there is a similar property for the video. If there is I would be interested to know since I might need it.