Though we are not trained to offer medical advice, we doubt that there any health concerns about such a trip as long as some common sense precautions are taken. There must be regular stops for restroom use, diaper changes, play breaks and the like.
Since toddlers demand a lot of stimulation, a portable DVD player may be helpful. Still, he will need to stretch his legs every couple of hours. Sunscreen is another must, as most car windows do not provide protection from sunburn. Children this age sleep pretty soundly on car trips, so that should not be a concern. If he is safe, happy and cared for, all should be well.