Lixxie,
Abs are important to us, especially as we age,so no, you cannot get away without doing them ...but a "normal" personal trainer will not know what you can and cannot do, especially with adhesions, scar tissue, incisions that can heal funky etc...I have worked out all my life and even then after each surgery my biology seems to change and what I can and can do does too...you need to get creative and not do crunches if they are causing you problems...
I now use the huge yoga ball and a vollyball size silicon ball...I start with the large one and drap my back over it comfortably and roll around over it (my back cracks back into place while I do this) then I slowly do tiny lift of my upper body, I also put my legs against a wall (or my sofa) and push back an forth while balancing on it with my back (hand off of the floor once you get your balance)...it takes a while but once you start you will find tons of interesting movements to do that do Not hurt you and that muscle you up quickly...I started in April and by the end of the 1st week I was amazed at the difference...now 6 months later I cannot live without it. The smaller one I place under my lower back and do all sorts of leg lifts, sissors (side to side, front and back) and other movements, fanny lifts etc...works wonderfully and no stress on my back of abs...just results.
Look it up on the internet and you will find tons more.
Sharon

This might help http://www.fitnessprospector.com/?p=888

Thanks. Stomach is still pretty sore when I use them, which is pretty unavoidable. Starting to revert to my old post-op tactics, ie. lifting my weight with my arms, and rolling sideways out of bed.

I wonder if I should see my doc about it, but not really sure what he'd do.

Why don't you try asking for 2 or 3 sessions with a physiotherapist? Just to teach you what is good and bad for you and give you correct instructions for your back and abs.
Sharon