A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data
Excel doesn't handle a spill range in the 'Applies to' box of a conditional formatting rule (yet - perhaps it will in the future).
You can create a rule of type 'Use a formula to determine which cells to format', with a formula such as
=AND($C2<>"",ISODD(ROW($C2)))
and apply it to the maximum possible range covered by the spill range. In this example, C2 is a cell in the top row of the spill range, in a column that is guaranteed to be filled by the formula.