It depends on the crank set and what the chainline of the hub is. IGHs that use 3 spline cogs have around 5mm adjustability as you can flip dished cogs around, or run a non dished cog as required.
I've done a large number of conversions, and have always managed to zero in on correct chain line using a combination of cog flipping or axle spacers to move the chainline one way or the other, and square taper BBs at the short end of the spectrum, like 107 or 110 mm.