Fixed. It was Mircosoft and their bloody wording in the error message I never proceeded with the install past the pre req as I figured there was no point if it was going to fail populating the System Management container with data. I noticed after my post above RC2 has been released so I thought I'd give that whirl instead thinking it was probably going to be a longshot but you never know.
Anyway, it all comes down to the way Microsoft worded their error between RC1 and RC2.
RC1 error:
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Warning; The site server is unable to publish to Active Directory. Check that you have granted the site server's computer account full permissions to the System Management container in its Active Directory domain.
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RC2 error:
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Warning; The site server might be unable to publish to Active Directory. The computer account for the site server must have Full Control permissions to the System Management container in its Active Directory domain.
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I decided to proceed anyway and hey presto, all good, the System Management container populated with data.