Short answer to my own question is yes, Canvas.drawPath does use the clipping set on the canvas as well as the shape of the path itself, it does not overwrite it.
theCanvas.clipRect(new Rect(632, 269, 1265, 539 ), Region.Op.REPLACE);
theCanvas.drawPath( theNativePath, thePaint );
The above code produces my path, painted with my texture, but within the combined area of the path and the rectangle I applied to the clipping in the canvas beforehand. My texture still looks wrong, but the issue is not with the clipping, it behaves as intended.
Upon further investigation this morning I've narrowed the problem down to something I've done wrong with either the BitmapShader in the Paint object, or its an issue in my texture cache which supplies the BitmapShader.
Apologies for any confusion - I will now put on the 'dunce' hat.