Bonjour !
The answer is NO, BUT :
1) not very useful : as any piece of a straight line can be graphed with one equation, so you may graph each error bar !
2) better : if the point set in Grapher comes from a Numbers or Excel or OOo or NeoOffice table, it is very easy to add two more (y1), (y2) values list to the first one (y0) ; y1 = y0 + n% or y0 + k y2 = y0 - n% or y0 - k ; enter this in Grapher point sets and you'll get maximum, minimum, medium for each x value and three curves instead of error bars.
See examples in attached files.
Au revoir, YB24