Yes, of course this is possible. You can add a single product to as many projects as you want.
To add a product to one or more projects there are two options. The first option is to go to the product sheet. On the left hand side, when scrolling down, you will find the project information. You will be able to see to which projects the product is added and if you click at the blue « Add to Project » button at the bottom you will be able to ad the product to more projects.
A second option to add a product to a project is by clicking on the « folder icon » right below the product picture.