Don't worry about warnings, just ignore them.
After you open an .ACB file you can previev the animations only if you copy them in a new animation worksheet; after this, click on a blank zone of the worksheet: you will notice in the object inspector 2 options, "creature rig" is the option you need. With this option you can choose a creature to use to preview the animations.
Then right click over an animationtion you want to preview and choose "play"; choose "reset" to stop the playback. Looking the previews make the things more clear to understand.
The 2 blend trees you mentioned, are problably used by the engine, becaues the doga_humov, groups the animations applied to Humanoids when they are overwhelmed by a creature and the animations of deathblows against creature.
The doga_dlg seems to groups 2 idle animations used during dialogs.
.ANB files are made by "post to local" the animation worksheet, in the "Tools"-->"Export" menu.
See you soon