It is not true that you "require" linked mode for SRM.
I wrote that blog specifically outlining that it is *not* required, because SRM shows you a consolidated view of DR from either site, regardless of whether you've used linked mode or not.
If you *want* to use linked mode then you have to use multisite SSO, and indeed as mentioned above, that is mostly because of easier license sharing and simplified login views.
But SRM does NOT require linked mode, let's be clear!