No with only XenServer, you can enable WLB but it's only to distribute your host resource better between your VM.
CloudPlatform is the product Citrix sell for that. (autoscale with your host)
Check step 3. You see that it manage your host.
When the CloudPlatform user submits the AutoScale configuration, the
following events occur:
- CloudPlatform uses the NetScaler NITRO API to push the AutoScale configuration to the NetScaler appliance, creating AutoScale-related
entities on the appliance. The entities include a load balancing
virtual server, a service group, and monitors.
- The AutoScale engine on the NetScaler appliance sends API requests to CloudPlatform to initially deploy the minimum number of virtual
machines required.
- CloudPlatform provisions the minimum number of instances (VMs) on the hypervisors (virtualization hosts) that it manages.
- The NetScaler appliance discovers the IP addresses assigned by CloudPlatform to the newly created VMs and binds them, as services, to
the service group representing them. The NetScaler appliance can then
load balance traffic to the VMs.
- NetScaler monitors bound to the service group start monitoring the load by collecting SNMP metrics from the instances.
- The AutoScale engine on the NetScaler appliance monitors the metrics collected from the VMs and triggers scale-up and scale-down
events whenever the metrics breach the configured threshold for the
specified period. As part of the scale-up trigger, the NetScaler
AutoScale engine sends an API request to CloudPlatform to deploy a new
VM. After the virtual machine is deployed, the AutoScale engine binds
the service representing the VM (IP address and port) to the service
group and, after the configured quiet time, starts forwarding load
balanced traffic to the new virtual machine. Likewise, as part of the
scale-down trigger, the NetScaler AutoScale engine selects a VM, stops
forwarding new requests to that instance, and waits for the configured
quiet time (to allow for the processing of current requests to
complete) before it sends an API request to CloudPlatform to destroy
the chosen instance.
In this way, the NetScaler appliance monitors the application and
triggers scale-up and scale-down events on the basis of application
load and/or performance.