The cries of foul would still be made if he avoided the inquiry appearance by Calling the Election, that'd be a very useful piece of ammunition to opponents. That's why I dismiss the suggestion of March.
Cries of foul there may be, but they wouldn't achieve much. The election will be fought on the issues and the platforms set out by the parties, as the Conservatives have been successful in doing thus far. It would be far more effective NOT to refer to the Chilcott Inquiry (or make allusions to the fact that the PM may have used the election as a means to avoid giving evidence). By referring to the Inquiry and the legality/illegality of it, the Conservatives would risk drawing attention to the fact that they themselves voted for it in the House.
Having done a little bit of investigating though, there's no reason at all why the PM couldn't do both, ie., give evidence to Chilcott Inquiry and have an election on 25th March. If the PM gives evidence on either of those two dates suggested (3rd or 4th March), the earliest date upon which an election could be held (calculated according to the 17-day timetable suggested by Parliament) would be 22nd March (21st March being a Sunday). Equally, I should correct myself with regards to Easter. There no longer exists any legislation that prevents the election being held on Maundy Thursday (1st April). If one sets aside any moral or religious convictions and principles, then the PM could appear at the Chilcott Inquiry on 3rd or 4th March, dissolve Parliament anytime between 4th and 8th March, and hold the election on Maundy Thursday.
Of course, those dates and timetables all assume that the election will be held on a Thursday out of convention. There is no legislation or statute that expressly requires that an election must be held on a Thursday. If so inclined, the PM could pick Wednesday, 31st March as Polling Day. All of the results would be known by the close of business on Thursday and Parliament could effectively remain shut until the following Tuesday to take account of the Easter recess.
It may also seem a gamble and a tad suicidal to call a General Election so quickly after giving evidence at the Chilcott Inquiry but if the polls reflect the current narrowing, the gamble on the PM's part would be that it can't get much better.