If the question implies to run a selenium grid in the same kubernetes cluster as the applications that should be tested with it, there is no problem with that. There is also a helm chart to spin up a selenium hub with several nodes quiet easily https://github.com/helm/charts/tree/master/stable/selenium

The only thing to watch out for is while scaling your applications or the selenium nodes not to steal resources from each other.

You can work with taints to separate your application resources and your selenium resources on different kubernetes worker nodes to prevent that.