MacBook Pro HDD in Gparted - Main partition "unknown"
It all depends on how the system you are running GPARTED from is configured.

It has been quite a while since I have used the Ultimate Boot CD but if I remember correctly it did not have built-in support for HFS+ filesystems. In other words GPARTED will work with HFS+ partitions (create, modify, delete, etc.) but I am unsure that it supports mounting an HFS+ filesystem.

The Ultimate Boot CD Wiki has no listings when searching for "HFS." Literally nothing comes up. So either their search function is completely messed up or that CD does not offer HFS+ file system support. 

And if trying to mount that file system fails with an error it seems likely that there is no HFS+ support on that CD.

Depending on how Linux knowledgeable you are there are HFS+ filesystem implementations available for Linux that you may be able to install on the Ultimate Boot CD but tht would be outside my area of expertise and outside the remit of AskDifferent. Perhaps over on https://superuser.com/