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If I am fielding a Deathguard army detachment which has cultists in it, and a CSM detachment that allows me to use the CSM Strategems, can I use Tide of Traitors which is a CSM cultist specisific strategem on the cultists from the Deathguard detachment?

I see no where in the rules which forbids me from using stratagems from one detachment on units from a separate detatchment.

To my knowledge, there is currently no such Restriction.
Many feel there should be, so it might change in the future....

PS:
Someone even raised the fact many Stratagem lacks the terminology 'friendly,' and thus nothing prevents you from using them on your Enemy for... odd results.

There is no confirmation that it is a CSM cultist stratagem specifically. It has the words Chaos Space Marines but that may just be the detachment you require to qualify for it, such as how Alpha Legion stratagems exist too. The rules for what defines a Chaos Space Marine detachment may bleed over into defining an Alpha Legion detachment and so it is purely for qualifying to have the stratagem at all.

The only restriction stratagems currently have is the targeting. Chaos Cultists is a specific unit... but it does not say CSM Chaos Cultists. Much like how people were arguing in favor of Helbrutes from Forge World, it is entirely possible to use Chaos Cultists that are not CSM. Technically, it also doesn't say "friendly" Chaos Cultists so there's room to argue that you can use the stratagem on your enemy's cultists to banish them to the corner of the table like the traitors they are.

Some might come here with arguments about Death Guard being specifically banned from using any of the rules or abilities in the codex... but those rules and abilities aren't being used by the Death Guard. The stratagem is used by the player who owns a CSM detachment and merely targets a Death Guard unit as a psychic power would.

Short version: Yes.

As I figured.

Since the Death Guard and The Heratic Astartes are members of the same army list, I can use Tide of Traitors on my Deathguard cultists.