Sure "/" will do fine too, that is also the way it is already fixed in the code. The variable with problems is only used in windows version to avoid right restrictions.
For sure having to deal with '\' is a PITA (there is a lot of "escaping" code throughout the CIYAM project that is conditionally compiled for Windows although I would have thought that Java programs wouldn't have such problems).
If you write the property with java and then read it you will have no problem. This variable is written by advanced installer during windows installation and then read with java and that leads to problems here, because advanced installer writes it in this "bad way". Java itself does proper escaping of course.