Well sure, but generally I look at the motive and logic behind it. Cena won't go out of his way to be a heel unless provoked by someone else's heelish actions, Sheamus was going about and attacking Henry/Sandow unprovoked. One example that comes to mind is him bitching out of the arm wrestling contest to cheap shot Henry, who was just trying to follow the rules of the arm wrestling. There were other examples like that int he Henry feud and its continued on to the Sandow feud.
They are definitely trying to make that a part of Sheamus' character IMO, much moreso than a guy like Cena.
I think in some way, there is a logic that if you perform a heelish action against a heel (without toeing too far over the line, like assaulting his girlfriend/wife unprovoked or anything), it's acceptable because the heel is a douche and he 'had it coming.' I've always compared it to the way it's somehow OK for a baby face to use the title on a heel in a match so long as the heel tried to use the title first. If Del Rio brought the WHC into the ring, for example, and tried to nail Ziggler with it but Ziggler kicks him in the gut and then picks up the belt that Del Rio dropped and slams it into Del Rio's face and then pushes the title out of the ring and covers him for the pin, that's seen as acceptable (and plenty of faces have been guilty of it, including Cena)... Whereas if Ziggler was just frustrated he couldn't pin Del Rio and/or just wanted to finish him quicker so he went out to grab the title himself from the time keeper to put Del Rio away immediately, that would be seen as cowardly and cheating, or in other words, 'heelish.'
In some way, I think the way Sheamus often cheap shots heels is seen as the same type of logic because Sheamus doesn't really perform the same actions against fellow baby faces, only heels. Even if the heels don't wrong Sheamus first, there's that feeling they could or might (since they're heels and it's what they generally do) so Sheamus is just getting the first shot in.
