The Olympus 5050z uses pre-flash to set white balance, so your YS 50 would fire on the preflash -- and not be ready for the main flash. In short, it would not work for the 5050z. You will probably need a new strobe.
It's a challenge for an underwater camera to communicate with an external underwater flash reliably, and a second challenge to support the pre-flash/flash operation which many digital cameras need. Loosely speaking, there are two ways. The flash can either sense the camera onboard flash output and mimic it, or use the camera's hot shoe signals with some custom electronics (more on that later). Ideally, for true TTL flash exposure you want to use the hot shoe signals, but the PT-015 case does not bring them out, so that's not easily possible.
Different strobe makers have different solutions to this problem. Most build sensors which observe the camera onboard flash and signal the external flash to fire at the same time. Ikelite does this with a "wireless TTL" sensor which sends an electrical signal to its digital flash via copper wire (guess that wire doesn't count?). Sea and Sea DX models use a fiber optic light pipe to sample the onboard flash optical signal and reflect it to the optical trigger on its digital flash. In both cases the flashes are special for digital cameras, in that they can double flash for the preflash and main flash. (Older flashes, including the YS-50, can not reliably be ready for the second flash, unfortunately.) The Light and Motion Tetra 5050 housing takes a different approach, bringing out the camera hot shoe TTL exposure signals to a bulkhead connector on the housing and firing their flashes using those electrical signals and copper wire cables to their flashes. Unfortunately, the housing alone costs US$1500, and the flashes are rather expensive too, so this elegant solution which allows full TTL flash control is beyond the reach of many of us.
It is announced that Olympus has developed a special UW flash housing for its FL20 flash and the necessary slave trigger electronics to control it, but only for the 5060 and later cameras. For now, it seems there are only two reasonably priced solutions for the earlier models: the Ikelite "wireless TTL" sensor solution using their DS-50 or DS-125 flashes and the Sea&Sea optically coupled solution using S&S YS90-DX flashes. These are available and work for many uses, although the S&S are actually operating as manual flashes with pre-set output levels, not TTL controlled.
I will be experimenting with a new gadget that reputedly solves that problem and allows full TTL control flash with the PT-015. Hopefully this will take some of the guesswork out of operating the camera while diving and yield better images than I have been getting with my current setup.
