Yes. If by diabetic vitamins you mean sugar-free than yes it is safe to take while pregnant.
No evidence of risk. A report in int j fertil. 1985;30(1):85-7 reports that there is no evidence that artificial sweeteners harm a fetus. Some of these do not even cross the placenta (aspartame) the report can be easily found on pubmed and you can read it in full but there might be more risk from dyes and fillers than the sweeteners. Discuss with your obstetrician if really concerned.