Combining multiple vCenters

Hi, I currently have 2 vCenters, one for PRD (6 ESXi 5.1.0 hosts, VMware Std, approx 50 VMs) and other for VDI (2 ESXi 5.1.0 hosts, approx 40 VDs).

Therefore I have 1x Trend Micro Deep Security Server (with 8 TMDS Appliances), 2 vShield Manager Appliances

I do come into many issues when I update the ESXi hosts where I will need to maintain 2 sets of virtual machines (VMs & VDs).

Is there a way for me to combine such that I only use 1 vCenter ? Is it quite a straightforward operation and would I need downtime for the Virtual Desktops ?

What are the drawbacks ?

Thanks for the advise....