Against, as NetRadiant aims to be mostly code compatible with GtkRadiant, as long as there are other GtkRadiant forks out there that may have features NetRadiant could use.
If I did a batch change to change all these ifdefs, patches will be unlikely to still apply.
What I can do is add robustness by adding -DWIN32 to the compiler command line when building a Win32 build.
Actually, I just checked: the Makefile, which is an 1:1 port of the previous SCons based build system, always adds -DWIN32 when doing a Windows build. So in NetRadiant, this is just fine. Anyone adding a Visual Studio project has to read the Makefile anyway, as NetRadiant consists of lots of subprojects that need different compile settings (e.g. because there are multiple header files of the same name). I know it's ugly, but it matches what Id Software released as GtkRadiant and I'm not going to change that as long as there are other merge-worthy Radiant forks like DarkRadiant.
BTW, I just merged NetRadiant's q3map2 with VorteX's changes to the Urban Terror map compiler fork.