The investigation by the Committee on Standards in Public Life will include an examination of the spin row which has led to calls for the resignation of Stephen Byers.
The transport secretary's former spin doctor, Ms Moore, and Mr Sixsmith, the transport department's former head of communications, both lost their jobs as a result of the 'Spingate' affair.
Asked who would be called to give evidence, he told BBC Radio 4's Today programme: "Certainly we have not drawn up a list yet but I would not be at all surprised were Ms Moore and Mr Sixsmith on that list.
"I would be surprised if we did not see them.
"It is up to them to come, to see whether they want to talk to us, but I would hope they would because I'm sure they can give us some useful enlightenment."
'Blair saved Moore'
Later he added: "Special advisers are specifically exempt from the requirements of impartiality and objectivity [applied to civil servants].
"Some recent cases have highlighted, however, that uncertainties and grey areas remain concerning roles and functions."
BBC Political Editor Andrew Marr told Today it had been suggested to him that Ms Moore, who previously faced calls for her resignation after her notorious 11 September e-mail, stayed on at that time on the say-so of Mr Blair.
He said: "Stephen Byers was quite willing to see Jo Moore go and then worried that it might set a worrying precedent and I think - fairly clearly - did get in touch with the prime minister and the message came back 'you hold on to her'."
Meanwhile Downing Street has confirmed that Cabinet Secretary Sir Richard Wilson is to have his say on what should be included in a government civil service bill.
A report in the Times newspaper says he will suggest a strict limit on the number of advisers employed by ministers.
Byers pressured
It adds that Sir Richard will also set out what he believes should be the limits of their remit.
He is also expected to propose an independent watchdog to police the new rules, with the power to investigate apparent breaches and report to Parliament.
"We are relaxed about it but it needs to be made clear to the electorate what such and act can and cannot do."
But he stressed: "No legislation can deal with internal feuds or civil servants not keeping to their code of conduct."
Ms Moore was accused of regularly breaking civil service rules by interfering in the appointment of officials or ordering them to act politically.
The pressure on her former boss, Mr Byers, continues as veteran Labour MP Tam Dalyell joined opposition calls for his resignation.
'No punch pulling'
The standards committee will also examine the central charges that the civil service has become acutely politicised.
Sir Nigel has already said he supports the idea of a Civil Service Act to clarify the relationship between ministers, their special advisers and civil servants.
Cabinet Office Minister Chris Leslie said the government had been talking about producing a Civil Service Act for some time and had already produced the first code of conduct for special advisers.
The Conservatives have said they will support a Civil Service Act.