If you use the generated OTO, BGM means that you have a consistent offset at the beginning every time, so really the only adjustment needed is when the detection is off-time (ex. vowel strings, y/w strings, m/n strings...) So while it is possible to bundle a BGM and base oto with a new reclist, only the BGM is necessary since a well-versed OREMO user will be able to generate their own base OTO.
The upcoming English VCCV™ is going to come with a base OTO because it's not a hiragana japanese reclist. So if you intend to do something like develop an Italian CVVC reclist to be recorded in OREMO with guideBGM, creating a base OTO to fit the timings would be beneficial to end users.