Sorry, no. At least one station (either the origin staion or the destination station) of your train journey must be located outside an individual towns PlusBus travel zone or city-wide region (such as: Greater Manchester; South Yorkshire; West Midlands; West Yorkshire).
If you are travelling by train from Dewsbury station to Sheffield station and want bus travel in Sheffield, then you can buy PlusBus ticket. This is because Dewsbury is in West Yorkshire and Sheffield is in South Yorkshire. However, you cannot buy and use a PlusBus ticket if your train journey is between two local stations that are within the Sheffield PlusBus travel zone (e.g. Sheffield and Meadowhall), or between two stations within West Yorkshire (e.g. Barnsley and Dewsbury).