Do NOT remove any DCBF directories manually
Theorectcally, you can by using the command
omnidbutil -remove_dcdir [directory_path]
but, they are not taking up any space. Now that you have "DCDirAllocation=1" set, the DCBF files will start being equally allocated. As a user, there should never be a reason for you to go into these folders
My advice is to just leave them alone. Perhaps, think about doing a 'writedb/readdb' in the near future, as your output from 'omnidbutil -info' shows some moderate IDB fragmentation
Finally, I noticed that you are close to max'ing out your 'fnames.dat'
Extension file "fnames.dat3":
Device = E:/Program Files/OmniBack/db40/datafiles/cdb
Maximum size = 2096128 [kB]
Current size = 1870016 [kB]
You should probably, proactively, create a new 'fnames.dat' extension file, especially if you are not planning on doing a 'omnidbutil -purge -filenames -force' or a 'writedb/readdb' anytime soon.