I personally do not believe ethics and morals are relative. But for the sake of this particular argument, they are. If we are to proclaim that a specific game (or any other form of media, for that matter) is unethical, we need to ask 'from whose viewpoint is it unethical- why does it matter?', and 'if it is unethical, what do we do about it?'
The first question is theoretical in basis. By whose standards are we calling war games (and by extension, war and its representations) unethical? People have different feelings about war, and about WWII. Some people feel that all violence is immoral, others feel that wars are bad in general (but WWII was a more just conflict than most), and a small minority believe that war is inherently glorious. People who view WWII as ultimately a just conflict against a foe that was quite evil are going to be more comfortable with the current way WWII games are made than people who take a more nuanced view. Also important are the roles that these games play. For many people, they are simply entertainment and nothing to get worked up over (this is the view most people seem to be taking, and it is the one I am inclined towards). Others feel like games provide meaningful social commentary and that their players do form opinions about history, warfare, and WWII in part by playing those games, and that the views these games espouse are distorting those opinions.
The second question is where people start getting touchy. Most democratic countries have free speech laws in place that allow developers to depict historical events in the form of video games in pretty much whatever manner they want (Germany may be an exception). If we do agree somehow that WWII games are immoral, unethical, or simply disrespectful, what are we to do? Boycott game developers that make those sort of games? Petition for better representation of the horrors of warfare? Simply refuse to play those games? And how should other people respond? Unfortunately, video game companies are in the business primarily to make money (just like movie studios, or the companies that publish books). If arcade-fun morally simplistic action-hero style WWII games sell (and they do), why should they bother changing up the formula- especially since it is almost guaranteed to reduce sales? To whom do they hold an obligation to accurately represent historical events- to their shareholders? The people who buy games? The people who make them? Or do war veterans simply deserve this obligation by the virtue of the sacrifices they have made? Ultimately, why does the debate matter- what are we going to do about it?