I'm not knowledgeable enough to answer your questions, Pat. Until someone who is responds, I'll offer you a couple of observations which are only intuitive, but seem reasonable.
I doubt that cremation was common with regard to WWII casualties. The facilities for such would have been limited, whereas burial could have been readily accomplished in the majority of cases.
To my knowledge, there is no web site that will contain specific info about wounds received during the war. Certainly nothing which parallels the enlistment database, or the databases of those who died during the war.
To proceed with any hope of success, I believe you will need to first establish his unit, to the lowest level possible. With that info, you (or others whom you hire or otherwise work with) may be able to access unit info contained in sources such as the National Archives, unit veteran associations, or the like. A brief insight into the type of resources available can be seen at this web page: http://www.archives.gov/st-louis/military-personnel/morning-reports-and-unit-rosters.htmlhttp://www.archives.gov/st-louis/military-personnel/morning-reports-and-unit-rosters.html
If you can also establish the date of his wounding, you should be able to get unit history that tells you, at least, what his outfit was doing, and where they were doing it, at the time his was hit.