hot spares are global, they are not designated to specific pool. See attached doc, there is a section on hot spares.
I have a VNX that was originally populated with 10K drives only, with 2 10K hot spares configured.  Some additonal 15K drives were recently added.  The pools are not going to mix drive speeds, so all pools are either going to be all 10K drives or all 15K drives.  I would like to add a 15K hot spare but want only the 15K pools to use it, and likewise have the existing 10K pools only use the 10K spares.  Is there a way to configure this in Unisphere or will the VNX use any available hot spare when needed?  If that is the case is there any built in logic that prefers a spare matches speed if one were needed?
VNX - allocate hot spare to specific pool?