I wouldn't do that. First, you connecting together two different raid groups (1 and 5), which impact performance and limits your iops to raid5. Assuming that's your local storage, performance could not be an issue in that case, but there are still some things you should point your attention. If I've understood well, imagine, please, that something happens with any of the disk in any raid. With that, you can loose you data completly, no matter their location, since you aggegated you datastores. From data security perespective, however, you still have got 1 "spare" disk (exact copy for raid1 and parity for raid5), thus you can survive one disk loss in particular raid.
If I were you, I would create global hotspare first, then create 1 volume (raid5, for instance) build from remaining disks. You can still survive 2 disk loss (combined hs and raid5 parity) with no confusion and datastore mess, still having quite good performance. I assume all disks are same size and speed.
Hope it helps.
