Currently the new ePub 3 standard allows for the embedding of fonts so for the most part, your fonts will look perfectly fine but there is a caveat to that. For fonts to be successfully embedded, they need to be either Opentype or Truetype fonts. Your designer will be familiar with these. Now this is an everything or nothing thing. If your manuscript consists of any other type of font, then all bets are off and then the fonts viewed on an ereader will default to whatever default font resides on the device being used.