I think the Domina Vacanze rumors predated Alejet and entourage going to DV. With Alejet, Zabel is completely unnecessary and in fact would not have a role.
I think Zabel is a good target for one of two types of teams: (1) a team that is interested in marketing extensively in Germany, and who would like to take advantage of Zabel's high popularity as a celebrity figure and cyclist in Germany (like Gerolsteiner or maybe even Liberty Seguros), OR (2) a team that is "on the brink" and doesn't have Protour status and that is using Zabel's past success and name to try and make sure it get into the TdF or other Pro Tours (as an invited team) -- somebody like Ag2r or Sella (the team that Rujano is on, as insurance in case their Pro Tour application does not get accepted and they have to rely on invitations).