In fact, this depends on which Hyper-V server you wan to manage from your Windows 8.1 client.
This post indicate it's totally possible to manage a Hyper-V server on Windows Server 2012/R2 from the Windows 8.1 Hyper-V Manager.
Now, to manage Hyper-V Server 2012R2 (standalone), it's a bit different. This post explains how to remotely manage such an installation, either with Powershell, Server Manager or an MMC console. This article indeed state that you will have to install the proper RSAT if you want to manage your installation with server manager (point 1.2).
If you want to manage an Hyper-V server on other version of Windows Server, please refer to this article, which has a table to explain the compatibility of the Hyper-V management tools.
Hope this helps !