OK, I can confirm that using:
OPEN TE-BUTOVO-B4?minplayers=20?maxplayers=32?Difficulty=1
creates a functioning single player (and presumably a listen server - I can't test this at the moment) game with me and 19 bots whose behaviour felt like difficulty=1. I tried substituting TE-OGLEDOW_B9 and TE-PROVKHOY_B1 and was similarily successful (please note that Butovo has a dash before the beta suffix while the others use underscores). I'm going to see if I can get the Univermag running but I attribute any problems with it to its alpha-ness.
I can also confirm that the invisible bots you can hear but not see are the result of mis-spelling the ?minplayers=X variable in the console (I forgot the 'S' and had the same result as you with your space...
I hope this helps,
Fafnir_6
EDIT: I can't find a working Univermag DL link so I guess we'll just have to wait for the first BETA release (which is probably for the best). I would trust BOH-Rekrut since he is responsible for many awesome Darkest Hour maps as well as the increasingly popular TE-BUTOVO-B4 for RO2. This map will RULE when it is finally released properly. I should also note that LordGleedo looks to be poised to release the BETA1 of his new map this weekend (should be good :)). I'll be sure to post the download links for any new content in my news thread...Stay tuned.
KRT_Bong check your PMs