Yes. Cross-Sell does not turn off your Related-Items and can be displayed simultaneously.
There are several combinations available to you. You could, as above, have both Related-Items and Cross-Sell displayed.
If you preferred to turn off your theme's Related-Items and just display Cross-Sells, that is possible too.
We also offer a 'Toggle' option. When a product page is loaded this will automatically detect if that product has Cross-Sells assigned. If it does then those Cross-Sells are displayed. If not, your theme's Related-items are displayed instead. This way only one set of items is shown at any time.
Please let us know if you would like your current configuration changed to any of the above. We'll be happy to help