If the host is in the same vcenter cluster - then vcenter will do the vmotion for you, vcloud just sits on top of this.
Normally for resource issues you just add more hosts to the cluster that is backing the vcloud provider (up to 32 hosts).
However if you are trying to go from one VCD provider (backed by a vcenter cluster) to a different one... well you can but you need to STOP the vapp. Move it. (I normally use the copy function in vcloud) - then you might need to make some chanegs to the network bases on how the new provider works. And start it back up.