I think what is going on here is both expected behavior and an exercise in learning a little terminology.
It is normal for a Mac to see a third party created RAID array as a single disk (which I am assuming it does) In both the Finder and Disk Utility? Why? Because the LaCie utility is designed to create RAID arrays that are completely transparent (or if you prefer invisible) to the operating system.
The converse is also correct, if you create a RAID array with Apple Disk Utility the LaCie utility will just see it as a single disk.
I work with Windows/ESX servers at work and RAID is created in the firmware of the RAID controller, before the operating system even loads. So both Windows and ESX see the RAID slices as individual disks even though the RAID array knows that there are 6 physical drives set up in a RAID-5 array.
There may be reasons to use the LaCie software over Apple's Disk Utility (or vice-versa) but I am not aware of the relative merits of each utility.
BUT You can be assured that what you are seeing (if I understand correctly) is entirely normal and expected behavior.