Not sure if you read this or not yet, but taken from the vuhdo wiki: http://vuhdo.ithato.com/VuhDo+Freque...Questions&bl=y

Q: What is the "Private Tanks" panel?

A: This is for persons you personally want to keep an eye on and so have them in an extra group. You can assign them by binding "menu" to a click-combo in Options=>Spells to bring up the context menu and then select "Private Tank" to add/remove someone from that list.

I've used that function for some time now but only for pve. The author seems to reply quickly to bugs/feature requests on curse, maybe try there if you can't figure it out still. best of luck!