The new cluster you are merging onto does not vMotion between the old one so in the regards you should be fine. New deployments will "pick" a cluster to go to, they will not move between. Keep in mind this, they will NOT move between - so at a later date it is not simple to remove the added cluster (at least while you have content running you need).
Check:
Hardware version - I assume you are using VMware HW8, just make sure both server types can run this (most can).
Cluster size... if using fast provision on iscsi or FC, make sure the total size of the ePVDC is 32 hosts or less (both clusters combined) - if not using fast provisioning this does not matter. (This is due to a linked clone limit of 32 hosts pointing to a single source)
Will your content work - This one normally hits with linux VMs, If created on the first set of hosts, and added to a catalog - if the destination hardware is very different you could have issues with the VM (all comes down to how the linux kernel was built and installed) -- Normally we see issues when the hardware is VERY different.
To be safe I would (if possible) do a small test, maybe one host of each time and make sure content works; but the feature is designed to do what you are wanting... the ability to add hardware of a different type in order to expand the pVDC to have more resources.