At the top of the web page it states: "raise money for handgun control, inc. every time you shop online". I believe this means that when you buy from a listed merchant, they give some money to HCI. To me, giving money implies support.
SAS has an affiliate deal with Omaha Steaks as well. These companies have neutral policies, for the most part, and are giving $$ based on referrals. Same as Amazon.
They're in business tomake money, and probably don't care about the politics of whom they are involved with...