Its possible to upgrade VCSA 6.7 to 7 without upgrade ESXi and stay on 6.7.0 ?
Can we have some problems if we do it ?
Thank you for your helps.
Yes, that's possible. vCenter Server 7.0 supports ESXi 6.5, and later.
However, in case that you are using e.g. vSAN, it's recommended to keep vCenter Server, and the ESXi hosts on a matching version.
Yes definitely is possible to do the upgrade of VCSA without upgrading the ESXi even by following the documentation you will see that is a pre-requisite.
You will not face any issue related with functionality at all. Just a thought for the future is that you always need to remember that vCenter Server supports two ESXi versions before which means that once you upgrade to version 7, the minor version of ESXi you will be able to run is 6.5.0.
I am giving you this example as when VCSA 7.5 (or whatever number they choose) got released, if you want to upgrade, it will probably support ESXi as it last version.
Finally, always check the VCSA 7.0 and ESXi 6.7 (updates included for both) release notes for possible known issues between those versions.