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.
If it's clean ice (clear ice is strong, cloudy ice is pocketed with air and its week) and a minimum of 4" under foot you'd be alright. I've fished over two inches of ice before but I was only tipping the scales at 150 lbs. That raises another point; never ice fish with fat people, choose your ice fishing friends wisely. I have fat friends that love to ice fish but I'm not going on the ice with them.
Two things to note: Number one bring a light weight friend and number two carry rope but never tie yourself and friend together, you don't want both of you falling in. On the topic of walking with a friend, don't walk together. Put some space in between you as you make your way out there because if you're both in the drink, your screwed.
Enjoy the Hard Water Fishing, and if you're of age don't forget the whiskey. It's about the only thing that warms a person when the winds are cutting through you like a steely knife.
Thank you for the advice.Never done it but wana try it.Last I checked there was 6-8 inches n I only go 150 lbs. myself. Probably won't go the tip up route as I don't wana invest the money if I don't like it.My friend isn't heavy either n were takillya drinkers but we'll b careful out there.Again thanks,the pics on the Diamond Lake website really got me,wana go....