The only obstacle is the hill itself as you enter and leave the trail system. It has some narrow switchbacks and a couple of ledges, but shouldn't be a problem for either of your vehicles. Once you're over the hill, the trails are sandy, scenic and easy.
I've got some great pics from a trip we took out there a couple years ago. We took a Dodge Ram and a Long bed F-250 Quad cab. Both made it without damage. Their clearance may be a little better than the FJ Cruiser, but the wheel base issues should equalize them a bit. Make sure you use a spotter to avoid undercarriage damage and you'll be fine. As for getting stuck, it's pretty much a non-issue. They have put pavement in all the difficult spots so that most stock SUV's can handle it.
My buddy in the Dodge did have to replace some suspension parts afterwards, but he liked to baja his truck, so he earned it. Beautiful area. Enjoy!
