I've messed with virtual machines before, but only with XP (MS is pretty lenient with keys there). I have a legitimate Win8 Upgrade key for my desktop, and an Acer OEM key for my laptop. My plan is to install 8.1 inside VMWare Player (or Workstation) as the Guest OS, while my Host OS on both computers would be Linux. I'm curious as to what options I have available for activation though? Would using my legitimate keys not work and/or possibly flag them? Do I have to use "other" means of activation?
You can use your Windows 8 Key and do the phone activation. As long as your key is genuine it allows unlimited phone activation. Because you are answering the MS System that you are re-installing it.
Legally: You may not use the Acer OEM key in the virtual machine. OEM keys are bound to the hardware and not transferable, even from physical host into a VM on the same machine. However, you may use your Win 8 Upgrade key inside a VM, as long as you are not also using it on a physical machine. The upgrade key is a retail key, and it gives you the rights specified in the retail EULA, which allows transferring between PCs. Practically: The upgrade key will activate over the internet fine inside the VM, especially if you haven't previously installed it on many different computers. Whether the Acer OEM key will activate inside the VM or not depends on several factors, such as whether it's an OEM: DM key or an OEM: NOSLP key. Either way, you can install it, and try to activate online, which may not work. However, you will be able to activate it over the phone, if you haven't shared the key with other people/other computers.