I think you need to look into why Veritas is not cycling the logs - that's the point of a full backup system in the first place.
Writing scripts to whack logs out for you is not a good idea - if for whatever reason they can't cycle the logs for you, you can turn on circular logging to prevent the transaction logs from growing - but clearly it's best to do full backups that cycle the logs.
The maintenance guides for Unity have more information on using circular logging and such - you can get them for all versions of Unity here:
http://www.cisco.com/en/US/products/sw/voicesw/ps2237/prod_maintenance_guides_list.html