It is common for many supplements to not be added to prescription drugs, especially SSRI's.
As for Alpha-T2, the only known effect on serotonin (not necessarily the only though) is the Rauwolscine HCL ingredient. Rauwolscine is a 5-HT1A receptor agonist.
Agonism of this receptor can decrease depression, decrease anxiety, help lower blood pressure and heart rate, etc according to what I have read.
Alpha-T2 should not be used with an SSRI because you do not want to have competition with your prescription on those receptors. Alpha-T2 also is not marketed to treat any type of disorders associated with anxiety or depression just because it has an agonistic effect on 5-HT1A.
But as for info to take back with you to the doctor, tell your doctor there is an ingredient that contains a 5-HT1A receptor agonist and he/she will understand what that means (hopefully).