, Yes you can manage ESXi 7 nodes with vSAN enabled with a vCenter 8. The nodes/cluster would of course not be able to use any features added in vSphere/vSAN 8.
Edit: re-read your question - why would you have a vSAN 8 license applied to a vSAN 7 node? This won't be applicable, use a vSAN 7 license for these unless the vCenter is version 8, if you upgrade the vCenter to 8.x you can use a vSAN 8 license (on only this) on ESXi 7.x nodes.