If your source only contains service accounts, you can create an Identity Profile attached to that source to import service accounts. Your tenant can have more than one Identity Profile for different types of identities.
If your use case is more that you want to have your service accounts in ISC so that you can correlate your accounts, you can create a file source with an Identity Profile to be able to create the identity. Check out this link from a recent presentation: Creating Service Accounts for SailPoint API Automations - Content / Video Library - SailPoint Developer Community