This depends on a few other factors...
Does your existing stack have IOM3 or IOM6 modules? or a mixture?
If the stack has IOM3 modules anywhere, you probably would not want to add this shelf to that stack. Always avoid mixing IOM3 and IOM6.
If they are all IOM6 modules on the existing stack, how many shelves are on the stack?
If there is only 1 or 2 shelves on the stack, and you do not have more SAS ports available, you should be fine.
Do you have the SAS ports available to put the SSD shelf on its own stack?
If yes, and you don't need those ports for anything else, put the SSD on thier own stack.
If mixing, you should try and have only a single transition and I always make sure the SSD is only one hop away from the controller:
For example:
SAS
SAS
SSD
Or:
SSD
SAS
SAS
Not so good:
SAS
SSD
SAS
