I read your first post to ask if two audits, one internal the other external, could be run at the same time. This way your internal auditors could take advantage of watching and learning from a professional consultant. For this I would say yes, a good idea.
As I read your second post, I got the impression that you would like to use the outside consultant's audit to supplement some missing Internal Audits. I believe that you would get both "Yes you can." and "No your can't." answers on this. I am from the camp of "Maybe.". For instance, Barb's question as to whether you procedures are written in a way that allows you to utilize 2nd or 3rd party audits as part of your internal auditing program. You would need to make a provision if you plan to do this.
A month or so ago, there was a pretty good thread discussing whether or not it was o.k. to use external auditors to satisfy 4.17. Lot's of good debate on the topic, I would suggest reading that thread for specifics. You will need to determine which way you would like to create your auditing program around.
For me a paradox: I believe auditor objectivity is the most important auditor characteristic, independence second. If you believe objectivity is the most important, then I feel you could use 2nd and 3rd party audit results (provided your procedures say so). If you believe auditor independence is most important, then you would be of the mind that a 1st party audit is different from a 2nd or 3rd party audit. The ISO standard mentions the word independent in it. If this is the case, then I would agree with your second post that external audits are not internal audits and the use of external audit reports as a supplement (complimentary, definately) is not advised. Sorry to be so wishy-washy on the answer, but I am still gathering information to put me on one side of the fence or the other. Back to the group...