For sure you can create a heatmap at cluster level, we have the metrics built-in to the MP for that
Take a look at our MP Help Center http://helpcenter.veeam.com/mp/70/vmware_guide/index.html?welcome_to_veeam_mp_for_vmware.html
In Appendix I. there is section on using our widgets to create dashboards.
You can copy the format of our Host Compute heatmap dashboard, and use two panes - one for Cluster CPU, and one for Cluster memory.
In heatmap configuration -
Use Group "VMware Clusters" for scope
For Tile class use "VMware Cluster".
For the size of CPU tiles ,use property "Total CPU GHz"
For the colour of CPU tiles, use metric VMcluster- cpuUsedPct
For the size of memory tiles ,use property "Total Memory GB"
For the colour of memory tiles, use metric VMcluster- memoryUsedPct
Let us know how your heatmap efforts work out!