http://www.sbs.com.au/news/article/2014/04/08/comment-east-asias-history-war-hits-australia
According to this article, women were forced to work as sex slaves for Japanese soldiers during World War 2. What about men? There must have been some men who were forced to worked as sex slaves. It would not be pleasant to make a sex slave pregnant.
Yes, definitely. Walter Dempster, also known as Walterina Markova, is a well-known example in the Philippines. His life story was the subject of at least two biopics.
There were more like him, though I can't find any sources that attest to how many male sex slaves there were.
Ronald D. Klein (13, August 2006). "Markova: Wartime Comfort Gay in the Philippines"