HP currently only has support and compatibility with Windows operating systems and requires Internet Explorer (or the HP ALM/ QC explorer) to utilize QC/ ALM. As far as is known (and HP doesn't release their future plans) they are only going to continue to solely support Windows operating system environments.
Not all is lost, though as there are options available to your users if they wish to use their Apple systems. ALl of which would require the use of virtualization.
These options all require Intel based processing systems (which covers everything produced sine early 2008 by Apple) and all but the last (which still has compatibility issues) will require a valid copy of a Windows OS.
Your users can install a Windows environment using the Apple built in system of Boot Camp (an apple supplied option that allows the installation of native Windows installation, and the availability to select the Windows partition upon start up, using the Option selection at boot time. See your Apple documentation to use this option). This requires booting into a native Windows environment.
The users can also create a windows environment on their drives using a third party virtualization software that runs within the Apple OS environment (no need to reboot into a Windows environment). Several of these softwares are available to accomplish this (some of the popular version of this virtualization software is VMWare Fusion, Parallels, and Virtual Box). This option allows the software to run both versions of operating systems at the same time.
The last option that I am aware of would require a software package such as CrossOver or WIne. These software packages are designed to run Windows applications natively under an Apple OS environment. This option is the least desirable of all the options. It doesn't require a windows operating system to be installed, but has very limited compatibility, and I am not even sure that it would run HP products due to the limited compatibility and constant changing environment of the HP upgrades.
The first two options are the best options available to your users.
I hope this helps answer your questions,