I would not recommend yerba mate' for autoimmune disorders. The problem is that mate' contains caffeine, more in the roasted than in the raw. Caffeine weakens the adrenals, which is half of the cause of autoimmune disorders. The other half normally being a microbial trigger. In the case of Crohn's and ulcerative colitis the microbial trigger is mycobacterium avium complex (MAC).
The adrenal glands role in the prevention of autoimmunity is through the production of immune modulating corticosteroids. In proper levels these help the immune system to produce specific high affinity antibodies. A lack of corticosteroids leads the over production of nonspecific low affinity antibodies. Low affinity antibodies tag healthy tissues for destruction by white blood cells because the antibodies cannot differentiate between true antigens and healthy tissue. Caffeine and other stimulants weaken adrenal function leading to lower corticosteroid levels and elevated levels of low affinity antibodies.
In addition Crohn's and ulcerative colitis are inflammatory conditions. Inflammation is also controlled by corticosteroids produced by the adrenals.
The reason yerba mate' helps with the bleeding and mucous is because of the high tannin content. Tannins are astringent, which controls bleeding and mucous production, but they do nothing towards treating the autoimmune condition.