It could be a bit of overkill having them both, however Hopes' recent outings with the ball suggest he is all but capable of being relied upon for 10 overs, infact I reckon he's less likely to be flayed about than Stuart Clark. And the fact he had a decent to good VB series means he cant really be cut loose right now.Watson and Hopes in the same team, ITSTL.
For me, I'd be happiest to leave Watson out - I don't see Hopes as a long-term option - until whichever time Hopes has to go. Obviously, right now Hopes has an unequivocal case for selection. In the meantime, put Hopes in the role you see for Watson - opening batsman and fill-in bowler.
Mind, I'm still far from convinced about Watson as a ODI bowler, though his batting has looked better in recent times. He was absolutely awful for quite a while, and while he's been a bit better of late, still far from outstanding.
With the bat he was extremely ordinary down the order for ages of course, and despite his excellent World Cup (3 not-out innings at strike-rates well over 100) at seven, I'm still far from convinced about him in that position. As an opener, though, he's certainly worth another go.
However theres no way he's as equipped to open the batting as Watson is, Hopes has some nice shots against the quicker bowlers, but that is all, does not possess an outstanding technique or great powers of concentration and as has been said if its a slowish pitch or the spinners are on he looks like a rabbit. Watson on the other hand has all the tools to succeed opening in one day cricket. I've long held the view if he were to do well anywhere in the ODI lineup it would be opening.
His bowling still has question marks over it however in my proposed side he wouldnt neccesarily be a frontliner, you'd need 10 overs from him/Symonds/Clarke.