The Rule Engine does not have access to iCal events. Feel free to create a feature request though! We already have support for processing the iCal format for dashboards, so in theory it could be extended to the rule engine. 
Edit: It looks like there’s a recent feature request for it here that you could cast a vote on and perhaps reply with your use-case to bump the thread.
There’s been quite a bit of discussion about this recently on the SmartThings community and it seems like people are using various approaches. There are a variety of solutions specifically targeted to the rental space that some people have switched to - I can’t speak to what solutions are recommended or if people are finding them to be good replacements, but you might search the RBoy threads in the SmartThings community.
SharpTools is a general purpose rule engine and is not specifically targeted to the rental space, but some people have found that their PMS supports sending webhooks based on check-in times or other events and they can use that with HTTP Triggers in SharpTools rules to build out the logic they are interested in.