Dear Tim,
It is not as bad as it sounds, however, the problems you are facing with SUM should be corrected in any case. To be more specific, hdbupd updates the database only. The HANA Client, HANA Studio (repository) and the hostagent are not touched by hdbupd. Especially in distributed systems, SUM takes care that all these components are updated on the other hosts too. Outdated clients and hostagent in turn can cause problems. If you have to do that manually, you require access to OS level in order to install these packages which is not always available.
In conclusion, it will be easier and less error-prone to update the database in standardized SUM environment (once it is set up correctly).
Best regards,
Michael