Well I think there are really two different things you have to think about.

1) How you are going to populate your user data

2) How you are going to handle authentication

OOB the LDAP/LDAPS connection handles both 1 and 2. Assuming you're on AD, SN's integration runs a scheduled import of all users in the specified containers/OUs and a listener for newly updated users as well as checking the entered password against what the AD server is holding.

The only thing you will be able to use the ADFS integration for is authentication. It interfaces with the Servicenow SAML 2.0 plugin to allow SSO with your AD user and Service-now instance. As far as I'm aware Service-now has no way to utilize ADFS to import users OOB. If you want to transition off an LDAPS integration for the import, you can always use a MID server to bring the user data (assuming you're on Dublin) or another method (ftp, sftp, et al) to grab flat files for the import data.

Configuring ADFS 2.0 to Communicate with SAML 2.0 - ServiceNow Wiki

Someone can correct me if I'm wrong, but there shouldn't be anything stopping you from using both at the same time as I believe the SAML plugin authentication attempt would supersede the LDAPS authentication attempt.