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.

The rock-pop boyband sold five million records at the start of the millennium, scoring number one hits with Year 3000 and What I Go To School For.
But Simpson walked out after a record-breaking 12-night engagement at Wembley Arena, saying his time in the band was "like torture".
Busted will pick up where they left off,  playing Wembley on 11 May, 2016.
The reunion was sparked by a road trip to Philadelphia, where the trio - Simpson, Matt Willis and James Bourne - recorded "three or four" new songs.
"I was astounded to find out James had actually been listening to a lot of the same music I'd been listening to," said Simpson. "When I left the band in 2005, we were worlds away creatively.
"It was quite poignant to think that we'd landed 10 years later and there was some creative common ground."
"It was just a really fun time," added Bourne. "It felt like we were just hanging out with old, good friends."
The band announced their comeback at the Soho Hotel in London - the same venue where they revealed their break-up in January 2005.
A dedicated group of two dozen fans waited for the band outside, after travelling from across the UK in anticipation of the reunion.
"It's magical!" said Rebecca, who had travelled to London from Ireland. "We're going to wet ourselves!"
"Busted are my entire life," said London-based Melissa. "They've always amazed me, no matter what they've done. Solo, in different bands, they've always been so good to me."
"It's been 11 years, nearly, which is too long to wait," said Roxy, from Oxford. "I feel like it's going to be different this time - because when they were Busted before, we were all kids and now we're adults. So it's a different audience they're going for."
Speaking at the press conference, Simpson said he was surprised as anyone by his return to the pop band - after carving out a successful rock career in Fightstar.
"I've lost count of the number of times where I've said publicly I wouldn't do this again. But I have changed my mind."
"We went to Philadelphia, we wrote new music and that changed everything. I was very ready to go to Philadelphia and come away thinking 'it just doesn't feel right'.
"The fact that it did feel right is just as much of a shock to me as it is to anyone sitting in this room today."
The band promised new material to accompany their tour, acknowledging that their back catalogue was currently rather meagre.
"Busted only had two albums," said Willis, who said the group would have to "play every song that you know then start all over again" on their 13-date tour.
When Busted split in 2005, they were one of the biggest bands in the UK, with two multi-platinum albums and two Brit Awards.
Simpson continued to make music, both with Fightstar and as a solo artist. Willis won the 2006 series of I'm A Celebrity... Get Me Out Of Here and appeared in the West End production of Wicked, while Bourne wrote songs for Melanie C, The Jonas Brothers and his own band Son of Dork.
In 2014, Willis and Bourne formed the seven-piece "supergroup" McBusted with the members of fellow boy-band McFly, releasing a top 10 album and supporting One Direction on tour.
According to media reports at the time, Simpson sold his share of the Busted copyright to his former bandmates for a six-figure sum to enable the supergroup's formation.
Speaking in London, the band confessed that the deal remained a grey area in their reunion plans.
"We haven't really spoken about that," Simpson said. "That's pretty low down the list of priorities."
"Charlie now works for us," Willis joked. "He's on a very tight leash."
Pelly Ruddock's second goal of the season for Luton all but condemned Dagenham to relegation from League Two.
[NEXT_CONCEPT]
Busted have announced a reunion tour for 2016, 11 years after Charlie Simpson left and the band imploded.