You need to install the hfsplus kernel module which, unfortunately, I think is not provided/supported by Vu so it is not possible to install it after an opkg update. You have to take the risk to find it and install it by yourself.
But, even after that, I don't know what will happen with disks already formated in MacoSX because it uses GPT instead of MBR.
As I am a MacOS user too for many-many years (since the time of MacOS 7), please allow me an advice: since we live in a "windows based world" format your external disks in windows based filesystems (preferably ntfs). It is much easier to read/write on it on every other operating system instead of trying to make all other operating systems to read an OS related partition. Unless you have the knowledge to do it, of course...