Creo should allow the creation of a datum plane simply through an axis without any other constraint.
This functionality is necessary for creating the sketch plane for a revolution feature around any axis (for example: Axis through point and normal to 3d surface). The orientation of the plane is not necessary for 360° revolution.
This functionality was possible in Pro/E 2001 version and before.
For workaround, we create these Datum Planes with ProE V2001 UDF (see picture).