Will Windows clients use DNS to map hosts to specific kerberos realms?
Specifically, do they use _kerberos.host.example.com IN TXT OTHERREALM.COM
records?
Windows clients only use SRV DNS records (and can fail back to NetBIOS-based discovery) to locate domain services, not TXT records.
I don't want to go in to too much detail about realm trusts and interoperability between Windows clients, AD domain controllers, and non-Microsoft KDCs because you don't say what exactly you're trying to accomplish... but you can specify non-Microsoft KDCs in the registry of your Windows clients in HKLM\SYSTEM\CurrentControlSet\Control\Lsa\Kerberos\Domains\KdcNames = kdc.otherrealm.com