Can the iPad play online video such as WNBA Live Access?
Yes but only through apps. Apple has no flash support so if there is a website that does not have an IPad app, then you cannot view the video
This is not completely true, as the iPad implementation of Safari supports html5, which (mostly) obsoletes Flash and makes it less relevant as more sites slowly adopt it. In addition, many sites will provide direct access to h264 video streams which MobileSafari's QuickTime plugin can handle no problem (just a week or two ago was watching the D8 conference videos on an iPhone).
HTML5 does not compare to flash, end of story
Besides the Youtube app, No