On your reader feature type, if you expose your fme_type or geodb_type I believe it will contain _ellipse if the feature contains a curve. From there, you can run it through a Tester or TestFilter.
In case you haven't solved this already you could try the GeometryPartExtractor with the following parameters:
Any polygon with an arc will be split up and arcs will be sent out of the Extracted port. See the attached workspace and let me know if you have any questions :D
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