Can I have two DHCP servers for IPv4/IPv6?

Solution 1:

Yes, these are independent, and the DHCPv6 server should also respond to v6 requests only.

If you use server software that supports both, you may need to explicitly disable responses to v4 requests, and you may run into issues if your DHCP server also updates local DNS (e.g. because an update flushes all records and then only adds records for one address family).

Also, the DNS settings handed out by both servers should be consistent.

If you don't need any features beyond address assignment, stateless autoconfiguration through router advertisements may be sufficient for you.