Hi Escapem2,
Yes it should be possible. There will not be any issue if you use two vendors for a datacenter or 1 VC from replication perspective. You will have make sure all the configuration requirements are satisfied.
In VMware replication, you will have to install vSphre replication appliance, same is manged by using web client. On the other hand Veem replication has their on console where you would add your ESXi or VC.
Both these replication technologies are at VM level, it should not have any issue until you choose different set of VMs for setting replication job. (There will not be any conflict)
From management perspective VMware replication helps as it is managed by same web client which manages entire VMware infrastructure. But there will be some difference from feature set perspective.
I suggest you to first drill down why customer would like to go for VMware replication and take proper decision. But you can use both together.
Plz refer:
http://www.yellow-bricks.com/2012/09/17/back-to-basics-install-configure-and-use-vsphere-replication/
http://www.vmwarearena.com/2013/07/adding-esxesxi-host-or-vcenter-server.html
KB1522:
P.S.: Award points if it is useful/correct.