Yes, Cornerstone has the ability to import 3rd party certificates.

Go to the FTPS/SSL tab for your server. Click the Certificate Management button then click Import. Now you will see an Import Certificate dialog box. Here you will have the option to import a certificate and private key into one file (PKCS#12) or into two separate files (.crt or .key). You can also specify the location of the certificate by clicking the small box at the end of each option. Once you are ready to import the files, specify the password and name for the certificate then click the Import button. Now you will see the certificate that you just imported in the Certificate Manager and you will be able to use this certificate in Titan/Cornerstone.

For more information, see the Cornerstone MFT FTPS Public Key Certificate Quick Start Guide: