I've started using viz in tooltip feature in tableau 10.5 and found that their is no option to hide the sheets that are used in tooltip. If we don't hide them before publishing to server, they'll appear as individual sheets after publishing in server. So, little workaround is to drop them on the dashboard as floating objects and set the height, width to 1 and X, Y position to -10 and also ensure that no borders are set, then they can be hidden.
Upcoming Tableau 2018.1 version has this option to hide.
I thought this might be useful to share.
Thanks for sharing, this will definitely help many people here.