If they are growing, then the roots have started pumping water and the vines are good. If they have not started growing, then the roots may not have started pumping water, and the exposed portion of the vine is as risk of desiccation (drying out). The lack of root activity could be due to several factors, too dry, poor root to soil contact, or may still be somewhat dormant. Like you said earlier, a good rain will usually solve the first 2 factors. Time will solve the last one.
As far as I know, all nurseries recommend covering the vines totally with soil to protect them from desiccation and from potential late frosts. It is not a big step in the planting process but can significantly increase the % take, usually to 100%, and it give the peace of mind that the vines are safe. Once the risk of frost is past, and the shoots are growing through the loose soil that is covering the vines, one only has to take a 4 prong hoe to pull the soil away and then install the grow tubes (if that is the plan).
I know that I have mentioned this in several different posts, but it is a lesson that seems to be difficult for people to accept.