My take on this: Prizes of the Dark City freely allows you to grant relics to Drukhari characters, as long as they are capable of being equipped with it.
The glossary at the back of our Codex states that an Artefact of Cruelty is a type of relic that can be given to Drukhari characters. Kabal, Wych Cult or Haemonculus Coven Relics are a subset of these which are only available to character models that are part of the respective Kabal, Wych Cult or Haemonculus Coven. Prizes will allow you to grant any relic that a Drukhari character is capable of having - this includes the Kabal, Cult or Coven relics.
A few supporting points here:
"Artefact of Cruelty" is not a keyword, and thus is informal. The book is clearly written so that we're meant to treat it as synonymous with "Relic" - indeed, the section where the subfaction-agnostic Artefacts are listed just has the title "Relics", and the language there freely slips between referring to them as Relics and Artefacts of Cruelty. We're not meant to see any real distinction between the two; for all intents and purposes "any relic a Drukhari character can equip" and "Artefacts of Cruelty" are equivalent.
The example used to discuss how relics can be allocated using Prizes involves subfaction relics. Without a clear restriction that this is only applicable in a Realspace Raid I don't see any way to read it except for allowing Prizes to grant subfaction relics in general.
Finally, as far as I'm aware most tournaments have followed this ruling- although I'll grant that it is rare to see sub-faction relics aside from Strife's being used competitively currently.