Qionized, Here is the straight answer you have been looking for. You should not have any issues updating the Dell Customized 5.0 to the Dell Customized 5.1. The issues you may have heard were due to updating from Dell Customized ISO 5.0 to the VMware version 5.1 (NOT Dell version), it was causing it to not see the NICS.  Let me know if this was what you wanted to know, or if you have any other questions.
we have a four host cluster with r620s.  vcenter and vum are already upgraded to 5.1.  i'd like to update the hosts using the dell custom ISO.  I've seen many threads that touch on this, but have yet to get a straight answer.  Has anyone successfully updated updated Dell Customized ESXi 5.0 -> Dell Customized ESXi 5.1 using VMWare Update Manager? Note: at present, hypervisor is installed to internal drives (not sd).
Update Dell Customized ESXi 5.0 -> Dell Customized ESXi 5.1 using VMWare Update 
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