The bardic music effect inspire courage doesn't offer a saving throw, so a typical creature that possesses the type plant—even if that creature had its type changed to plant via the feat Greenbound Summoning (Lost Empire of Faerun 8 and, by the way, a feat that's not without controversy)—simply can't typically benefit from any morale effects that a bard's inspire courage might provide. (Also see the example omitted from the SRD on Voluntarily Giving Up a Saving Throw that's on Player's Handbook 112.)
Examples of ways to eliminate or mitigate this issue include the feat Green Ear (Complete Adventurer 110) that allows a bard to employ a bardic music effect so that it affects only creatures possessing the type plant and the feat Music of Growth (Eberron Campaign Setting 57) that, in addition to other effects, allows a bard to use bardic music to buff creatures that possess the type plant in a way that's different from the bardic music effect inspire courage.