I saw a thumbnail to a Rogue One trailer and saw the Ghost ship from Rebels and even though the ship could just have a new crew aboard I wish I hadn’t seen it.
It’s very unlikely that it’ll be anything more than a very brief cameo, so I don’t really see the problem.
The only problem I have is that if it turns out the Ghost Crew is alive and well during Rouge One seeing that photo would undermine the surprise. If it does turn out to be a cameo like the Millennium Falcon being in ROTS then it won’t be an issue at all.