Solved! Go to Solution.
Short answer - yes
Longer answer - Your data must be in the same projection to be used in ArcPad. ArcPad can not add layers with different projections to the same map. The only exception to this is StreetMap or ArcGIS Online basemaps. Otherwise, ArcPad does not reproject data on-the-fly. See here for more information.
Hannah 🙂