You can do what you're suggesting, from I think the RAID controller in G3 and up. Before starting, I would upgrade the controller firmware (actually all server firmware) to the latest available from HP.
Also, once you've replaced the last disk and the array has rebuilt for the last time, (I agree with the prior suggestion for letting the rebuild go overnight) you'll have the options to either EXTEND the existing array or create a new array in the new space.
If you're trying to expand your existing hard disk volume in your O/S, you'll want to EXTEND the existing array, but you'll still be faced with the problem of expanding the disk volume(s) in your O/S. Is this a Windows O/S? i.e. right now looking in Disk Manager, your volumes are sitting on an approximately 165GB disk; after you extend the existing array, you'll see your same size volumes, with lots of empty space now on an approximately 330GB disk. Your disk volumes defined in your O/S will not automatically expand when you extend the array.
So now if you're using a windows O/S, AND you have at least 2 existing volumes with one as your system volume, then you can expand your non-system volume with DISKPART, but you can't expand your system volume.
Therefore I'd suggest using a server grade partitioning software like Acronis Disk Director to complete the job of expanding the volumes for your O/S.
