Yes, I have done it.
It is dead easy. Just install the SlackBuild the same way you would install any other SlackBuild. The only issue is that you might need to recompile the kernel before compiling VirtualBox (VirtualBox' modules need to be compiled with the same version of glibc that was used to compile the kernel, otherwise you risk having defective modules).
I prefer the SlackBuild because of two reasons. The first one is that it allows the package manager to handle the software. The second one is that the VirtualBox version in SlackBuild.org is open-source, while the binary version is not. The latter can be a matter of concern or not, depending on your point of view.