NovoLog Mix 70/30 - can I mix this insulin with novolin R sliding scale on the same injection side?

It is probably best not to. Both the insulins mentioned are slightly different. Novolin R is regular short acting insulin. It starts working relatively quickly, produces a peak in insulin levels, and then drops off relatively quickly. It is designed to help control the blood sugar spike that occurs after meals. Novolog Mix70/30 contains insulin aspart, a rapid-acting insulin, mixed with insulin aspart protamine, an intermediate-acting insulin. It is usually taken twice a day, with each dose covering two meals or a meal and a snack.
You should discuss this with your Doctor or diabetic nurse/educator.