Currently all our VM's are on fibre attached datastores in a HP Blade environment. If we moved to a VSAN or a hyper converged environment I assume there would be an outage as the datastores will no longer be shared datastores.
So I assume you would need to shutdown the VM and migrate it off to the VSAN/hyper converged environment or is there a way to present the VSAN/hyper convered datastores to your traditional environment?
With release of VSAN 6.5 you can expose your VSAN to hosts outside of VSAN cluster through iSCSI, see: http://www.yellow-bricks.com/2016/10/18/new-virtual-san-6-5/
Another option is present your current datastore to your new hyper-converged solution through NFS/iSCSI (if your storage array supports).
But, since vSphere version 5.1, you can migrate virtual machine between hosts even without shared storage, this is what VMware call shared-nothing or enhanced vMotion, see: Leveraging VMware's Enhanced Shared-Nothing vMotion - Wahl Network
So, the storage will not be the problem... I believe that you should worry about the processors compatibility, because if they differ, you will not be able to migrate online unless you enable EVC.
You can migrate from Fibre Channel datastores to your vsanDatastore using "XvMotion" (sometimes called "Unified vMotion") which was introduced in ESXi 5.1. This allows you to migrate VMs between ESXi hosts and datastores with zero downtime. Essentially it is a vMotion combined with Storage vMotion in single operation. You can do this between clusters, and even between different versions of ESXi. For example your HP blade cluster might be running ESXi 5.5 and your new VSAN cluster might be running ESXi 6.0U2. As long as you configure the EVC mode on the new VSAN cluster to the same EVC baseline as your existing cluster, you'll be able to perform XvMotion across clusters, from your Fibre Channel datastores to your vsanDatastore, with zero downtime. You must use the vSphere Web Client (not C# Windows Client).