If I add Little baron's creatures/undead/vermin to my bashed patch, does it need any BASH tags?
Nope - Just http://www.bild.me/bild.php?file=7488102Untitled0.jpg and Wrye Bash http://www.bild.me/bild.php?file=6586788Untitled.jpg if they conflict with anything (in my case with T.I.E). If they dont conflict with anything ... the mods esp is still adding them to your game.
They will randomly pop up in game, try walking around the edge of water for a while, those Water Dragon flowers will be sniping you're derriere with a fireball before long - If they are in a cluster of long grass they can be awkward to locate too for a few seconds. So you get a bit of a toasting before you finally home in and slap them.

@alt3rn1ty: Thanks for those links, I really like the undead updates. Is there a thread for his progress on revising the other two? PM me if it can't be linked to here.
I have never seen a dev thread for LB's work, unless he has one on TESNexus .. to be honest I have never gone looking for one would be nice to know actually what plans are in progress for Vermin and Waterbeasts - Hmm, I'm off searching

Edit: Some (but not all) of LB's are included in Creature Diversity mentioned above, but its a bit behind the curve with updates (includes for instance Ghouls and Mummies which has now been revamped by LB into Undead Additions), IIRC there are a couple of LBs creatures missing from the line-up, haven't used it for a while.
Edit2: http://www.tesnexus.com/downloads/file.php?id=26634
Edit3: Cant find anything dev for LB's mods.