Might be a long shot, particularly as I know there is an issue with binary storage of numbers but here goes - is there a way to check that a dwg file's coordinate system has at least 3 decimal places?
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You could use a CoordinateExtractor to grab the coordinates of a feature, then AttributeSplitter to split it on the . and a StringLengthCalculator to calculate the length of the last part, then test on that.
I'm not sure whether that's what you're looking for and if it is, you're still stuck with the fact that those are the coordinates reported by FME, which may not be the same as the ones actually stored in the file what with the storage of CAD coordinates (DGN would be a prime candidate for "problems" in this regard)