I’ve seen this done by some excellent tanks in vet trials. One particular example that comes to mind is vSO HM, where blade cloak can be used to help mitigate poison phase for the off tank holding the mantikoras. The quick cloak morph also helps to off tank get back to group quickly for bubble shields. So yes, it is definitely viable. Just make sure you do most of your blocking on your SnB bar and save your DW bar for buffs.