First of all the topic is shooting experiences with the Olympus 30mm macro V. the 60mm macro lens. The issue with the Olympus 30mm macro is VERY limited working distance and the port you are using. With my Nauticam NA-EM1 II the 45 port is recommended. In that port the front of the lens is about 10mm from the outside of the port glass leaving a working distance of about 10mm between subject and port at 1.25:1 or maximum magnification. Using say a plus 10 closeup lens would reduce the distance to 5mm plus the thickness of the CU lens would leave little to no working distance. In addition the CU lens would be at least 10mm from the front of the lens which would reduce the magnification of the lens because of the distance between the two lenses. Also the Olympus lens is already a 1.25:1 lens which at 1.25:1 is about the same amount of magnification as you would get with your Panasonic lens at 1:1 plus the ULC-165 wet lens. This is assuming that your lens is closer to the port glass on your housing. With the very best placement your lens at 1:1 plus the the Inon UCL-165 would get you to about 1.3:1.
For subjects the size of a Pigmy the 60mm macro is just the far better choice and at 1:1 you can use about +25 of magnification in front of the lens before the working distance becomes to limited. This would give you magnification of about 5:1 or a subject about 3.5mm on the long side.