They can donate whatever they want to whomever they want, but not-so-cleverly advertising their intent to do so with only a certain group would most likely be considered by the court to be de facto discrimination. The law requires you to not only treat your customers in a non-discriminatory way, but POTENTIAL customers as well. Intentionally not providing a wheelchair ramp does not prevent you from being sued by a person in a wheelchair who technically never engaged your services. Any gay person who sees that sign and interprets it the way it is clearly intended (that their business is not welcome there) has been discriminated against by that business. I’m not a lawyer, if you understand the law in question otherwise I’d like to hear your thoughts.