Using Roof Jacks w/ Wagon Caps instead of soil vent flashing

Quick question. A roofer in the area is using kitchen fan type exhaust vents or jacks http://www.homedepot.com/p/t/202191804?catalogId=10053&langId=-1&keyword=master+flow+wagon+cap&storeId=10051&N=5yc1v&R=202191804#.UjPrpj8hLkY instead of normal lead or auto caulk flashing’s on the sewer vents. To me this doesn’t seem right. Seems like moisture could build up, condensate and fall back to the decking given that the vents are larger than the pipe, and allow gas to fall back into the home. They could also allow small animals in. I’m not sure. Probably not a big deal but I can’t find any documentation on this. I have never seen or heard of anyone doing it.

I don’t think it is legal or advisable for “stink” vents. Fan vents, etc it is done all the time.

Probably not hurting anything but it’s definitely the exception rather than the norm.

I don’t think that allowing gas to fall back into the home is a good idea for the house.