Raw wheat has a gelatanization temp that is lower than that of the mash temp you will use for the barley. It will be converted in the mash.
Doing a cereal mash will give a better mouthfeel (according to Moaher0, and extraction by bursting the hard small starch granules making them available for conversion. This is the same as for a decoction mash using all barley, which gives slightly higher extract.
Where are all of the style/Reinheitsgebot police? Just kidding...