Unequal horizontal stab incidence will, as you suspect, result in a slight out-of-trim situation in roll. It would be best to fix it, if this is practical. Otherwise, it can be corrected by warping the wing very slightly in the opposite direction, but the required wing warp would be so small as to be almost impossible to measure. The aerodynamic rolling moment produced by 1/8" incidence difference between the two wing panels would be impossible to trim out fully by use of ordinary control surface in-flight trim, but the rolling moment produced by a warped stab, if it has, for example, 20% of the area of the wing, would be only .20 to the third power, or about .008 times the stab incidence angular error, if the stab has roughly the same shape as the wing.

A wing warp that requires holding a slight aileron deflection in flight can be trimmed out at only one airspeed. If you trim the model at low airspeed, at higher airspeed the ailerons will tend to be forced slightly back toward toward the centre position by aerodynamic force, since no control surface linkage or structure can be completely rigid. If you trim at high airspeed, the model will tend to roll in the opposite direction to the warp at low airspeed. I used to mess around with the tricky job of dewarping wings and fine-tuning stab incidence a lot. This job can easily require several attempts to get a model to trim perfectly at all airspeeds. Ground-adjustable trim tabs can fix this problem, and produce the ideal, a model that is in trim at all airspeeds.

I check for visually imperceptable wing warps by trimming at fairly low airspeed, then going to full power, and observing which direction the model rolls. It will always roll in the direction of the warp. I then land the model, make a small adjustment of the trim tab(s), and flight test it again. After a couple or three adjustments, the model should be in near-perfect roll trim. The same procedure can be applied to pitch and yaw out-of-trim problems, and produce a model that is a joy to fly.