Wouldn't venture out onto that ice myself - late season ice can be pretty thin and dangerous. And if you're fishing for trout (which is what you'd fish for at Diamond...) - you can only take them by conventional rod/line - I don't believe tip ups would count for that. You could verify that with a phone call to ODFW, or the OSP.
Personally, if I were fishing diamond's opener, I'd be looking for open water areas, or if I felt really adventurous, I'd smash my way through with a metal boat... or just wait for the ice to go away and fish then, and fish someplace that's ice-free.