This has been touched on
before.
As a former ScrumMaster myself, I am interested to see this happen, but we haven't really heard enough demand from users (or potential users) to justify adding these sorts of features. So if you know other people who are looking for this, encourage them to post here, or
contact us.
It would certainly be possible to create these sorts of graphs with some AppleScript pulling the data out of OmniPlan, but I suspect that wouldn't be much improvement over an excel spreadsheet. Plus, you'd have to do some weird mental math every time you updated OmniPlan. ("OK, Bob says there's 1 day of effort left on this task, and he started it 3 days ago, so I should make it a 4 day task and 75% done.") That starts to sound rather un-scrum-like, and I'm not sure what you gain from it.
What does OmniPlan give you that an Excel (or Google) spreadsheet doesn't?