You can limit your search to Rapid Rewards partners, and when you select a hotel, rates are listed as "Rapid Rewards rate" or "Rate not eligible for RR points"; I'm just seeing the latter on prepaid rates. If the rate isn't prepaid and you pay at the hotel, I wouldn't view it as a Southwest purchase for the purposes of RR Classic Visa credit. If prepaid, does anyone know who the payee is? I would guess the hotel rather than SWA.

Right under where you enter your RR number, they say "At checkin, present both your hotel loyalty number and your Rapid Rewards Membership number to receive credit for your stay." If it isn't a Hilton family hotel, they should just ask on which one you want credit if you do this.