I have vCenter 6.7 u3 in my environment, looking to add ESXi 7.0 on vCenter 6.7.
Can vCenter 6.7 manage/support ESXi 7.0
No. not supported - see the interoperability matrix: https://interopmatrix.vmware.com/#/Interoperability?isHideGenSupported=true&isHideTechSupported=true...
no, it's not possible
see this table
and this link
Product Interoperability Matrix (vmware.com)
The vCenter server version 7.0 can manage ESXi only in versions 7.0, 6.7, 6.5.
The vCenter server version 6.7U3 can manage ESXi only on versions 6.7,6.5 (some), 6.0 (some)
Some combinations have not been tested
Attached link to validate