They would be a negative for some quantitative finance jobs. Not because they make you a bad quant. There is a perception among practitioners (who are mostly math/physics PhDs themselves) and headhunters that web development people do not know enough math to be a quant.

To quote one well-known headhunter: 'Good point, there seems to be a correlation between "web design" and only ever having done fluffy crap of no value in this line of work. Of course, correlation is not fact but as a headhunter it is hard to avoid that prejudice'