There's an elephant in the room here I mean to address: The ritual requires a prisoner as target, who is aged and suffers brain damage as part of the ritual. Sort of sounds like they are the offering.
The problem I have with your theory is that, if Horax wanted one of your colonists, they could just take them. All of the rituals work by calling upon Horax, with them doing the actual work. The existence of the skip abduction ritual implies that Horax can grab anybody from anywhere on the planet. Given that Horax is perfectly willing to send anomalies to attack your colony, it stands to reason that if they had interest in random colonists, they'd just grab them with skip abduction.