With the new Lync 2013 server topology we now have the option of something called pool pairing, but what does that actually mean in reality.
Pool pairing is the ability to have one pool being the DR pool for the other and vise versa. This means with enabling the pool pairing option the secondary pool holds a copy of the CMS database and all the other nuances that are needed for things like conferencing and sponge groups etc. then in a DR situation the users automatically failover to the secondary pool (automatic means up to 5 minutes before the user sees presence again)
In truth I like this feature and it does work well in real life. A caveat to pool pairing you need to be aware of is the voice elements as the last thing you want is in a DR situation your voice calls start routing out of your secondly pool which you might have in a data centre in Asia etc. voice costs will spiral..
So what is supported from Microsoft. Quite simply is has to mirror the server and pool type.
Enterprise edition = Enterprise edition in the second pool
Virtual servers = virtual servers in the second pool
That said there is no technical reason that you can't have your primary pool as EE and the second pool at SE. (Common sense though if your EE homes 12000 users, then failing over to the SE which can only home 6000 users will simply not fly)
So if you want Microsoft support go with the mirror type approach, but in your lab you can mix the types to test the failover feature.