Is it true that dogs kept in outside kennells are generaly healthier than there house kept brothers.

Depends on the house really :)  If the house has smokers or the windows are rarely opened or central heating too high then, yes, I think they probably are physically healthier outside with adequate shelter.  Mentally, I think, it will depend on the dog and whether how much interaction they still get with their humans suits them.

I wouldn't have said it makes any difference at all providing the dog is well cared for, mentally and physically, properly exercised and the outdoor kennels are adequate.  I have outdoor kennels and two dogs that hate them.  I leave the patio door open for them in the warm weather and they come and go as they please.  In the cold weather, they're mostly indoors.  

Depends on every factor going.  When people say Kennels many normally think "not cared for, coped up all day" but a dog in a kennel could have plenty of own space, well looked after and have water 24/7  BUt the same goes for the house!

I know people who say their kennels are in better condition then their house.  ie clean, tidy, disinfected heating and A/C etc etc etc.

A dog kep outside will not be more likly to be healthier then a house dog!