Is my new iMac's tilted camera during video conferencing a hardware issue?

Welcome!

First, inspect the attachment point of the stand to the computer body for uneven gaps. If uneven, that could be a manufacturing issue.

This happens with camera set at 0.5x zoom (minimum setting)

That is likely a slightly wide-angle setting, and wide-angle on any photo device can cause some spherical aberration that may manifest as a tilt. Does the tilt persist when you set the zoom to 1.0?

Second, the work surface. I ask because one of our "work overflow" desks is not perfectly level. Affects the cameras.

What happens if you attempt to shim up one side of the stand, then the other? If it levels out when shimming one side and gets worse on the other, that could be a work surface or a stand issue issue.

The old engineer in me, conditioned to look at every potential internal and external factor, would also think, "I wonder if the bookcase is really straight?

In addition to what Allen is saying...

If the iMac is parallel with the shelf, then the shelf should appear lever and equal on both sides.

If the iMac is at an angle to the shelf, then the shelf will appear un-level or larger on the close side.