Is it possible to use CiviCRM tokens in external services?
Simple answer: No. Those tokens are expanded into text strings by CiviMail for each recipient and your third party service is not going to know what values to substitute for those.

Complex answer: Maybe.  If your third party service has a way to allow you to provide tokens for substitution, and you can generate the correct data and format out of Civi then you might be able to make it work.

But it's much easier just to use CiviMail!

If you are comparing CiviMail with another mailing service, do make sure you are using the Mosaico extension - it's way better than the old interface.