Hermione might be one of his allies. Despite their past differences, they could put aside their grudges for the greater good of the Horcrux hunt. Also, Neville could potentially be an ally. Neville has shown great courage and determination, and he might see Draco's newfound willingness to fight against Voldemort as a sign of change.
One likely ally for Draco could be Luna Lovegood. Luna is very open - minded and she might be able to see past Draco's past actions. She could also provide some unique insights into the Horcruxes with her rather unconventional way of thinking. Another possible ally is Ron. Although Ron has had a strong dislike for Draco in the past, if Draco proves his intentions are good in the Horcrux hunt, Ron might be willing to work with him. After all, they are all fighting against a common enemy in Voldemort.
In the 'Draco Joins the Horcrux Hunt Fanfiction', Draco may find an ally in Dobby. Dobby, being a free elf, has a strong sense of justice. He could see Draco's attempt to help in the Horcrux hunt as a worthy cause. Also, Professor McGonagall could potentially be an ally. She is a fair and just teacher who might give Draco a chance to prove himself in the hunt. She could also provide guidance and protection to Draco during the dangerous Horcrux hunt, especially considering her powerful magic and experience.