Yeah. The monitor and the PA will find a way to make a ground loop. If you are only ever going to play one venue, and you can prove that it's not a problem there, then you can just go with straight wire splits and be fine. If you want to be sure that you can get decent performance no matter where you set up, get yourself some transformers. I went looking for suitable unity transformers with the split built in (like a normal DI has), but couldn't find anything even close to affordable. A passive DI will actually work just fine. The step down in voltage is undesireable, but the little bit of extra broadband noise will be much easier to deal with than that incessant bzzzzzzz that comes from ground loops. It's not best practice, but it is standard procedure for about anybody trying to connect their laptop/mixer/active-whatever to the FOH.
That said: You know what i usually use to split signals? Well, somebody said patchbay earlier, and as it happens when I tore down the 7' rack and hocked all the hardware to go "all virtual", I was left with like 5 of those cheap modular 48 point patchbays. You know the ones where the box doesn't even go all the way around, and each module is just held in by the nut on the one jack? You're meant to be able to take them out and flip them over and reinstall to change the normal scheme. Well, I ripped those things out of one of the unused PBs, and use them all over the place. Keep a couple in my guitar case, a couple in my mic bag... They can be used to chain 1/4" cables together (who has a F>M cable when you need one?) or to mult signals. It doesn't sound like much, but they have been exactly what I needed to get the show going more times than I can count.