Just to be clear ... the mouse works fine in the Linux VMs if you connect directly from a desktop system to vCloud using the VMRC? (direct connect, no Citrix stuff involved)
Please be aware that Lab Manager and the vCloud VMRC are completely different.
Lab Manager's lets a user connect directly to an ESX host and uses WebMKS.
vCloud's VMRC routes through a given cell, and is more optimized for a WAN connection.