The one way I can imagine this working is to create a virtual switch (or contact sensor) in Hubitat, which is then shared with HomeKit via HOOBS. Then, within HomeKit, create an Automation that is triggered via the virtual Hubitat device. When the virtual device goes Active, open the blinds. When it goes Inactive, close the blinds.
I am sure some others who are more experienced with HomeKit can provide a more detailed suggestion.
