Actually ODB++ is a defacto industry standard and format is controlled by Valor (well, Mentor now). It can be presented either as a directory structure or as a compressed directory structure.
AFAIK ODB++ can contain stackup data too, another thing is if this data is exported by the CAD you use.
Thanks Artsiom, I agree with you. ODB++ is a quasi standard in the industry, broadly accepted by most, if not all major manufacturers. HKP on the other hand is proprietary and was not intended nor documented as a standard.
Craig, I would recommend to challenge CST, whether they are maximizing the usage of ODB++.
If CST is seeing any information gaps with ODB++, then we would encourage you to ask CST working with us understanding and resolving these potential data gaps.