Yes. Absolutely yes. One day you'll reboot and your partition table (and all your data) will be gone and unrecoverable. Trust me.
And that reason is that it *will* die horribly and eat your data. Set up the small logical drive in the RAID BIOS as another poster detailed so nicely. Now. Before now.
Thanks, that is what I thought might be the case.
*sigh* It's a good thing I found this out, however I'll have to do a painful migration of the data off that drive now and re-partition, etc which is just a pain. I wish Ubuntu had *stopped* me and told me the first time that *this is not possible!*.