With five matches remaining, the Daggers are 11 points from safety and could go down on Saturday if they lose at play-off hopefuls Leyton Orient.
The Hatters took the lead seven minutes before half-time when Ruddock's shot went in off the underside of the bar.
Jamie Cureton's shot was cleared off the line and Oliver Hawkins hit the bar as Dagenham failed to find a leveller.
Luton picked up their first win in four, but remain six points off the play-off places.
Pelly Ruddock's second goal of the season for Luton all but condemned Dagenham to relegation from League Two.