Data Architects are like Lawyers: you don’t need one all the time, but when you need one they are hard to come by. Because of this there is a growing movement in the software industry to have an architect on retainer.
The role of a Data Architect is to map out the foundation of the project and create the data models. At the beginning this may prove to be a role that is more than full time but, as the project moves along, the architect steps into the background until needed for more building tasks.
In maintenance mode your Data Architect is only consulted occasionally with the architect’s time mostly spent on new initiatives. This is a person to hire if you need them there more than 8 hours a week but, if not, putting one on retainer isn’t a bad idea.