It is absolutely NOT safe to use the same utensils on raw meat and poultry as on cooked. Either wash them thoroughly in warm soapy water in between, or do what I do: use two tongs: one to handle raw food and one for cooked.
Also, don't use tongs on raw meat and then on vegetables. Veggies may not be cooked long enough to kill off harmful pathogens. But you can use tongs from raw vegetables to handle cooked meat, since raw vegetables don't carry the same risks.
For more information, see Food Safety Tips for Grilling.