@Kitty
Puro-Puro
While it may not belong to the imps, there are 3 npc* that say that Implings are either related or the same species. As well you have ingame evidence with them both feeding of the wants and desires of mortals, they both have the same unique teleportation magic (Imo their teleportation magic is very important to imp lore) As well as imps protect implings in puro puro like guards or parents. Also the official wiki says
Tstanon Karlak, Destroyer of one thousand planes.
With jaws large enough to swallow an adult imp whole
Implying that there are non adult imps
With all that I would say its pretty safe to assume they are the same race but...
Say implings aren't baby imps or are demonized implings, and that they are just related, like a dog is related to a coyote, well that wouldn't make sense since all Avernic come from the fire, that would mean imps would not even be related in the slightest, and we would have two near identical species growing up on two different planets (Where ever implings came from), and then the imps randomly start protecting these little guys on their new planet for some random reason.
Souls
While I am hesitant to use the photo booth as real lore since it breaks to fourth wall, I don't really know about them taking your soul from a picture booth, heck Nomad should have got an army of imps and demanded that he needs team shots from every soul wars team.
Assuming it can be considered canon personally I think the picture taking ability is something they worked on so that they could blackmail, or plan hiests for valuable items.
22-Aug-2014 15:31:03