Can an artist come a set up their portable easel and paint?

It's under National Park Services (i think) and so I think they will be glad to accommodate portable easel.

I personally had seen someone drawing picture of flower so ,I think painting can also be done as long as it is not obstructing anyway .

I agree with DM Habib. It's open to the public and people are always taking pictures so why not painting as long as you are not obstructing access.