My employer demands boarding passes. This has been policy since before I started working here. Of course, I don't know how carefully someone looks at the documents, but I do tend to write an explanation whenever my ticket has been reissued. OTOH, upgrades aren't a problem and we're allowed to book our own travel and use personal credit cards, although of course there are per diem rules as well as rules regarding when premium cabin travel is allowed. It's my own travel budget so I'm incentivized not to waste money.