even if you did shim out your center spacer for correct wheel bearing endplay, you'd still have problems down the road since the powdercoat will break down over time, gradually loosening your hub anyway.
Consider this.... those fasteners that hold your wheel hub in place don't do so with shear strength - i.e. it's not the bolt that's holding them together, it's the friction between your two mating surfaces that keeps your hub on. If you have powdercoat on one surface you're effectively changing the material properties said surface and altering the way the fasteners themselves function. Not to mention that over time that powdercoat will break down, causing a loose hub which is even worse IMO.
I think you should consider bead blasting them and having that jackass re-coat them properly.
My .02
Edit: Also, if you use sealed wheel bearings the problem will be magnified since they are more sensitive to side loads than timken bearings.
I understand and I am quite familiar with residual torque vs. dynamic torque and asked several engineers beforehand and don't feel this will be an issue. Here is a nice read.
The need to measure torque doesn't necessarily stop when the assembly is finished. Manufacturers often audit finished assemblies to measure residual torque. This is a measure of the tension that remains in the joint after it has been fastened.
Torque auditing detects loose fasteners and "yielded" fasteners--fasteners that have stretched so much that they no longer provide clamp load. Auditing also detects joint relaxation. In many cases, torque auditing is the final judge of the harmony between the fastening tools, product design and materials, and the assembly process.
Residual torque can be measured using a power tool hooked up to a rotary transducer and torque analyzer. However, residual torque is most often measured using a transducerized electric wrench, a dial wrench or a preset hand tool, such as a click wrench or slip wrench. A click wrench has a calibrated mechanical cam that resists movement until a set torque is reached. A dial wrench has a spring that translates torque into motion on a calibrated dial.
Fastening experts warn that residual torque and dynamic torque are not identical. Residual torque is often lower than dynamic torque. In many cases, the joint relaxes after being fastened. Joint relaxation occurs to some extent in all fastened joints. One part embeds into another. A layer of paint, a spring washer or a soft part, such as an O-ring, compresses under the clamp force.
This relaxation, or creep, is most obvious and dramatic right after force has been applied. In most joints, creep appears within the first 10 to 50 milliseconds. However, some joints can take a long time to settle. Residual torque measured 1 hour after assembly can differ significantly from residual torque measured a day later.
"The farther away in time you get from fastening, the less likely it is that the residual and dynamic torque measurements will correspond" .
Residual torque can also be higher than dynamic torque. To test a joint after it's been fastened, the operator must overcome friction to start the fastener rotating again in the tightening direction. An accurate reading depends on the operator's ability to stop the moment he sees movement. "It's harder to get something rolling than it is to keep it rolling".
Another factor that can influence residual torque is "cross talk." This occurs when torque applied to one fastener affects another fastener in the same assembly. Changing the fastener installation sequence often solves the problem.
Because of these problems, fastening experts advise assemblers to avoid putting much stock in differences between dynamic and residual torque measurements. "Measuring residual torque won't tell you what caused the problem, only that there might be one". "It also can't tell you how good the fastening tool is."