No. An aggr should include LUNs backed by the same types of disks. You wouldn't mix SATA and SAS drives in the same aggr if they were NetApp disks, and you don't don't want to with array LUNs, either. Performance will suffer. it's possible, because ONTAP can't tell. But you should avoid it.
Re: Mixing drive sizes, but same lun sizes in same aggregate