Can a project split the source of renewable energy used on site between their own on site system and making up the rest through a purchase agreement with a community RES?

Example:

The project owner puts up enough solar PV on site to get to offset 1% of annual utility cost. They they purchase through a 3rd party the equivalent of 5%-10% more annual cost of community solar. Can the project achieve the additional 2-3 points using this approach?

Does the project still need to purchase RECs with this approach for the 3rd party supplied renewable energy?

Jason