When I had GD with both of my bubs - the first one was diet controlled at first and then needed insulin in the last few weeks.
My second baby I controlled it with diet alone, no problems.

My typical diet was:

Breaky - 2 x slices burgen bread with vegemite, cup of tea with one sugar

Morning snack - apple, some almonds

Lunch - Pasta with tomato sauce, OR burgen bread sandwich with ham and salad OR Vitawheat 9 grains with cheese and tomato

Dinner - meat and salad/veges, or pasta, or casserole with rice/pasta

Before bed snack - apple OR grilled cheese on burgen toast, glass of milk

That's a fairly rough guide - my diet was more varied than that I certainly didn't eat those same things every day.
The main things were I cut out all sweets and sugar (except for in my tea) and crappy junk food, and really heavy carbs like white bread and potatoes.
I found I was generally ok to eat most other things as long as I watched the portions. If I ate heaps of anything I would have a blow out, I had to learn to really cut down.
With my first pregnancy I was constantly hungry while on the diet which was why I ended up on insulin. I had cut down my food intake as much as I could and I was still over.
I never had a problem with my son, after a week or two I adjusted and it was all good with him.

By the time my GD was diagnosed and I started diet control my morning sickness was long gone. The GD was diagnosed at about 28 weeks, the morning sickness was gone at 10 and 14 weeks. There is a theory though that some m/s is caused by swinging bloodsugar levels and if this is the case I'd imagine that a GD-type diet would help. It's a healthy diet for pregnancy, whether you have GD or not so can't hurt to try.