If the records are visible to the Marketo user, you are technically able to send emails to them.
As for the compliance/permission side, that depends on if you obtain opt-in permission, especially for Canada.
If these people are you customers (and if they are entered by support, they likely are), under most of regulations (including GDPR), this is a sufficient motive for being allowed to send them email. It does not mean that you should use this as a free hunting permit, though
This is typically a situation where you should consider a sync filter.
- "Sync with Marketo" mysteries part 1
- "Sync with Marketo" mysteries part 2
- Instructions for Creating a Custom Sync Rule