A non-Segwit node can always validate transactions that are relevant to them. They do not validate the witness portion of Segwit transactions. They also do not generate Segwit addresses, nor do they participate in Segwit transactions. What you're talking about is moot.

The only real issue there is partitioning risk in the bootstrapping phase -- since Segwit nodes can't bootstrap from non-Segwit nodes. The solution for this (dropping non Segwit peers for Segwit peers in outgoing connections) has already been coded and merged.