The last Marion Mtn report on here was by Mountaingoat on 4/13/08:
http://www.mtsanjacinto.info/viewtopic.php?t=809
It's been a month so it's hard to say how much is snow is left. Not a lot of people go on that trail and even fewer report conditions on this forum.
The Marion Mtn trail is easy to follow if there is no snow. But if there is snow above Little Round Valley and you've never been on that trail before, it's very hard to follow because you're in a flat area and it's hard to find where it starts to switchback up the east side of the ridge. I remember my first time ever on San Jacinto was around this time of year a few years ago and Little Round Valley was full of snow. I had a map, compass and GPS but forgot to input the waypoints and I didn't have topo data loaded in the GPS. Without that data the GPS was pretty much useless other than recording my track. So I took several bearings with the compass and tried to triangulate my position on the map but this is only so accurate. Not sure why I didn't just plot the GPS coordinates on the map, LOL. I searched for an hour looking for the way up to the peak from Little Round Valley but could not find it. Turns out I was just 100 ft or so west of where I needed to be. If you have a GPS, I highly recommend loading it with waypoints from a route drawn in TOPO and topo data of the area. With that, it should be no problem to navigate up to the peak. If you don't have TOPO, email me and I'll send you a GPX of the trail.
My guess is that you might be alright and will be able to follow the trail but it's good that you're bringing crampons. I'd bring an ice axe too.