Networker 9 with VBA EBR appliance with vcenter 5.5

with new vcenter, you mean still an ancient, unsupported VCenter version? Also nw9 is no longer supported for many years by now, so wanting to make vmware based backups using VBA instead of the later vproxy appliance based approach, has been made obsolete for years by now. Heck, since nw19.6 restore from old VBA data is not even supported anymore if I recall correctly?

So an upgrade to a more recent NW version, using the vproxy based approach is out of the question? VC 5.5 is not supported in later nw19.x version, but slightly older NW versions would still support or better call it nowadays work with VC5.5, as there is no support anymore for anything in that sense, not for nw, not for the vproxy nor for the VC itself.

NW18.2 when it was still supported, supported these VC versions at the time:

VMware ESXi: 5.5, 5.5U1, 5.5U2, 5.5U3, 6.0, 6.0U1,
6.0U2, 6.0U3, 6.5, 6.5U1, 6.5U2, 6.5U3, 6.7, 6.7U1,
6.7U2, 6.7U3, VMware VMC on AWS: SDDC 1.6, SDDC
1.7, SDDC 1.8, SDDC 1.9, VMware vRealize Automation:
7.3.0, 7.3.1, 7.4.0, 7.4.1, 7.5.0

with Dell EMC vProxy version: 3.0.1-51 or even the older Dell EMC vProxy 2.3.x-x version.