I don't know, but I'm pretty sure it hasn't led to there being more disease up here. Perhaps they work on the basis that of you are putting a ram to all your ewes, you probably have taken care to ensure you know about its history and health before you do that. That's certainly the case with all the people I know who do it.
Also there maybe aren't so many sales outlets up here live auction wise, so standstill, ESP on a family partnership farm spread across several holdings using the same rams might get into difficulties. I'm sure it's on a risk assessment and risk benefit basis, as I say I think it hasn't caused major issues so why not, it's relatively small numbers and all tracked with movement docs.