After a bit of consternation I managed to come up with a pretty simple solution to highlight cells in a range if a cell in a different range has the same value:
=MATCH(RC,'Interactive Calendar'!C2,0)>0
What I'd like to do next, and I'm having some difficulty figuring it out, is to check if C3 in the Interactive Calendar sheet has a specific value based around location.
So IF =MATCH(RC,'Interactive Calendar'!C2,0)>0 AND the corresponding cell in 'Interactive Calendar'!C3="Brisbane", then format the cell. There are three locations, Melbourne, Brisbane and Sydney so the plan was to have 3 different formatting rules across the same area.