Is there an equivalent to this command on server 2008r2? I'm trying to configure the dynamics 365 App for Outlook and this command is one of the steps. It looks like it wasn't added until 2012r2.
No - because "The Add-AdfsClient cmdlet registers an OAuth client" and ADFS 2.0 has no OAuth support.
This was only added in ADFS 3.0 (partially) and the full stack is available in ADFS 4.0.