If I understand your question correctly, each member of a tech group is on a one week rotation to be auto assinged all the calls for that group, escalating to other members if necessary. To achieve this you were going to enable the vacation schedule for all member except the one on rotation. Problems occur with techs in multiple groups.
If you have techs on rotation at different times in multiple tech groups, I don't see how the vacation schedule could ever work.
Try this -
Depending on if it makes more sense to use tech groups or request types, I would make the tech that is on rotation for the week, either the group manager of the tech group, or the lead tech of the request type, and always assign tickets to either the group manger or lead tech. Seems more straight forward, bit less to manage than putting people on and off vacation, and I think this will work for what you are trying to achieve.
Thanks for your answer. We have appreciated it !
Switching the vacation schedule seemed to be a good idea since the tech may change its vacation state itself but in practice this is not usable, of course, and you've right !
Therefore when the Group Manager should execute some task once a week it would be better, when a conflict occurs, that (s)he takes the tech out of the group for that week.and includes it again at week's end.