we have already upgraded our vCenter to 6.7 U3 which we do not think it has any issues with Nutanix.
But to upgrade ESXi itself we do not know about its compatibility, i know about the case of patching ESXi to a higher patch level than the Nutanix certified ones "which we are regularly doing", but for ESXi 6.7 U3 we are afraid of breaking something or being incompatible, and we do not know either if ESXi U's are considered as patches or different versions according to Nutanix..
I searched over Internet and this forum about anything related to 6.7 U3 compatibility but found nothing, at least if we have a road-map from Nutanix about planned compatible version we can wait till its release.
Best answer by RichardsonPorto
As explained before, Nutanix will provide you support, but supported and qualified version are different things... and since on only the qualified version the Nutanix engineering tested the product, we cannot guarantee the same results if you upgrade for a non-qualified versions.
You are correct about some known issues with ESXi U's and this is because VMware made change in some API's that broken workflows from Nutanix side. One known issue for instance if the Field Advisory #58, where VMware made change on ESXi bootloader and affected a lot of workflows from Nutanix side.
To sumarize, if you want to be on safe side regarding Nutanix/ESXi, upgrade only to qualified versions that you can found on Compatibility Matrix list in our portal. But if for your stay on latest patches for security reasons is more important, go to latest ESXi patches and Nutanix will try the best to support you, but without guarantee that it will works the same way it works on qualified versions.