You're totally right.
This error message doesn't block anything about the SCCM related discovery (means writing discovered information in WMI and sending them to SCCM through hardware inventory). It's only block when trying to send information to RCS server. I heart that a known issue or I should say, its by design, that acuconfig can't send discovered information when the discovered computer doesn't already exist in RCS database.
The provisioning part of SCCM/RCS integration works great even with the error (the discovery TS ends successfully with warning so it's OK). I had some trouble for provisioning because I had at first a profile name with spaces in it configured on my RCS server. Once removed spaces, everything works flawlessly!