Not being 100% sure of your environment, except that you are getting intermittent ESXi crashes during higher IO loads (e.g. copy process of backup job), we would suggest checking the following VMware KB articles and see if one of them matches the diagnostic dump you are getting.
Per VMware the most common cause of this is when there are too many VMs using a E1000 or E1000e virtual network adapter. The work around reported by VMware is to change some of the VMs to use the VMXNET3 virtual adapter so as to reduce the number of VMs using a E1000 or E1000e virtual network adapter. Or, of course you could always apply the appropriate VMware patch.
http://kb.vmware.com/selfservice/micr...
http://kb.vmware.com/selfservice/micr...
We have gone back through our support history and have this logged one other time. Both the work around and the patch process recommended by VMware resolved the issue completely.
Hope this helps. Please let us know if we can assist further.