Among the 63 Nayanmars, 42 of them were poor farmers or thieves or vagabonds or hunters.
For example, Kannappa nayanar. He was a thief who attained relief from re-incarnation inspite of spitting on an idol of God and kicking it.
Komelakar, from the poor low caste man, who got preference beyond any brahmin or anybody in the court of god.
Nandanar, for whom, the Nandi moved and gave him the full view of Lord Shiva (and relief from reincarnation) is also from the lowest castes.
There are many such examples.
"Guganudan, aivaranom" - Kamba Ramaayanam. Which means, Lord Raama, embraced the boat-man Gugan and included him as His brother.
Valmiki was a thief before he wrote Ramayana.
Shiv Ratri, a major religious day, is based on a story when a hunter sent home a mother deer to feed its child and in the mean time, the hunter was unknowingly worshipping Shiva.
As astro said, Krishna was a cow-herd.
Pandheethan was a cook!
Vidhuran was born to a daasi.
Hindusim had a weakness through its caste system. However, there are many many stories where people of lower castes attained heaven and the blessings of supreme being faster than the so called higher castes.
To the best of my knowledge, I think Hinduism never had any slaves (I may be wrong). I don't know any stories about slaves attaining supreme glory.