Can you access a CentOS7 server from a CentOS6 machine?

My Background:
I have been tasked with upgrading our task management from Trac/BZR to Git/GitLab. I’m not familiar with servers, and although I’ve worked with Linux machines for several years I’ve never done anything as backend as this. Forgive me if the following is an out-of-place or too novice of a question.
Lab Setup:
We have a lab full of CentOS6 machines which we use for work. We are in the process of updating them all to CentOS7. At the moment only our server is upgraded to CentOS7 with hopefully only a few months until our work machines are upgraded as well.
If we go ahead and install/migrate/ect from CentOS6 Trac to CentOS7 GitLab on our server will we still be able to access that server using our CentOS6 Machines?
I’m not familiar with server hosting/access and want to make sure we’re not starting this process too early. Should we wait until all of our machines have been upgraded before we migrate servers or does the server/client relationship not depend on the running OS of each?

Thank you for your time,