I'm my chapter's Philanthropy Chairman and I've set up events with other GLOs. We never did anything big, but I think that it's best to do some smaller events to see if you could get along working on a larger project. You'll be happy to know that if you contact another house's philanthropy chair, they'll be grateful to have you and your members help.
For my house, when I set up events with sororities (I've never set up events with other fraternities) the guys are more likely to come out to the event
. Also, you should remember to try to get involved with orgs outside the ones in IFC and PHC, you should also try to do events with NPHC and MGC. The first joint-event that I ever planned was with Delta Xi Phi Multicultural Sorority Inc. We've made a lot of friends in that group, which probably would not have happened otherwise since the different councils don't really seem to interact very much.
Also, try to get involved with groups outside the Greek system, I'm currently talking to the President of Circle K who is delighted at the prospect of doing a joint-community service project. The important things is that you should try to do events with a myriad of orgs that have a volunteer/philanthropic focus.
By the way, I was just elected as Philanthropy Chairman of the Inter-Fraternity Council before summer, so I've begun planning events for all 11 chapters in IFC.