As much as I adore Playtonic, I don't think they have this grand idea and plan for every single detail. Voices, I suspect, are just mumbled off-the-cuff (usually by the very talented Chris Sutherland). Jon is a good speaker and has a funny voice; I don't see it ruining the game, or being particularly recognisable without prior knowledge.
I think the game has quite a bit to gain in terms of publicity by associating with him, actually. Maybe I'm adding too much importance to him though as I genuinely don't follow him or watch his stuff.