Alimony counts as income for SSI. This is because it brings in some income. Alimony is also referred to as spousal support, thus it goes through SSI. You can get more details on the SSI official website.
from what i recall, alimony can be deducted from income for the person paying it and must be claimed as income for the person receiving it. I would suggest you contact the social security office and inquire to be certain.