DSHS assistance in Washington State for Tenant

Landlord here... running into this issue for the first time.  My tenant called and asked me to set up a Statewide Vendor # so that DSHS (Department of Social and Health Services) can make payments for rent on the tenant's behalf directly to me.  The form to create a Vendor # also requires me to fill out a W-9.

I'm wondering if anyone has experience with a similar situation?  Also wondering if I'm taking on any legal risk by participating or not participating?  Any general background information would be much appreciated!  Thank you - Ben