Can Event ID 4013 be ignored if it only shows up once?

Yes you may safely ignore it, unless it keeps happening repeatedly long after the domain controller/DNS server has rebooted.

The warning should only occur when you reboot the domain controller or otherwise restart AD and DNS.

The reason this happens is simple - DNS hosts Active Directory-integrated zones, and therefore cannot finish initializing until Active Directory is up and running and healthy. But since you just rebooted, Active Directory is not finished starting yet. But Active Directory can't finish starting without access to a DNS server. So you see, AD and DNS are waiting on each other. (But eventually, a timeout occurs, a warning event is logged, and AD and DNS will eventually both start normally.)

The correct way to avoid this issue is to have more than one domain controller, and have each domain controller point to the other as its primary DNS resolver.

But if you're unwilling to add another domain controller to your environment, then you can safely just live with the warning events.

This is fairly normal for a single DC environment, due to the order and nature of components as they start up (the networking stack, DNS and AD) and the reliance of AD on DNS.

Do you see Event ID 4 and 2 after the Event ID 4013? If so, then everything is OK.

As a best practice, you should have at least two Domain Controllers and each Domain Controller should use it's partner DC for primary DNS, itself for secondary DNS and 127.0.0.1 as tertiary DNS.