Hello and Welcome to LQ,
You're in for a challenge if you want a mixed environment

.
Read this chapter at
Samba.org.
Somewhere down it states:
Quote:
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SAM replication with Windows NT4 domain controllers (i.e., a Samba PDC and a Windows NT BDC, or vice versa). This means Samba cannot operate as a BDC when the PDC is Microsoft-based Windows NT PDC. Samba-3 can not participate in replication of account data to Windows PDCs and BDCs.
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So, if you cannot replicate the account data of your users to a BDC, then you have no fallback, hence no BDC.
You're faced with some decision making in my opinion.
Kind regards,
Eric