I'm pretty sure it's in that -Djava.library.path also, but I'm a little slow today, what do you mean by the "usual quoting, escaping, etc."?
From what you described it is almost certain that the problem has something to do with the way that JDeveloper handles the vm parameter in launching the Java application.
It's not properly handling the path with the space in it. To try and fix this, try to determine the exact call to Java (as ra4king suggested). From here you can try different combinations of quoting the vm parameter, using a backslash in front of the space, or move the slick libraries to a location on your filesystem that doesn't have a space in it.