Cardi B admits she's a blood but not in Tekashi69's old set nine Trey

Cardi seems to be taking issue with her rep ... saying she is a Blood, but absolutely not associated with 9 Trey. Cardi explained, in a tweet, she's a member of the Brim Bloods set.

A rep for Cardi has denied the claim she's a member of the Bloods, telling TMZ, "This is not true."

Tekashi was eventually released, but not before they pistol-whipped him ... landing him in the hospital.

He's cooperating with the feds as part of a plea deal to get a reduced sentence in his own case. Tekashi had been facing a minimum of 47 years in prison.