Definitely. If anything, it may well be an advantage.
People often neglect the heavy constraints and disadvantages of the use of god-concepts.
Mystics by the term mystic don't believe.... But that has zero to do with atheism.For the purpose of this thread, we will use the following dictionary definition for 'mystic'...
"a person who seeks by contemplation and self-surrender to obtain unity with or absorption into the Deity or the absolute, or who believes in the spiritual apprehension of truths that are beyond the intellect."
https://www.google.com/search?q=mys...0l3j69i59l2.1043j0j4&sourceid=chrome&ie=UTF-8
There is at least one form of atheism that rejects the existence of Gods in favor of a higher absolute...
"Axiological, or constructive, atheism rejects the existence of gods in favor of a "higher absolute", such as humanity. This form of atheism favors humanity as the absolute source of ethics and values, and permits individuals to resolve moral problems without resorting to God. Marx and Freud used this argument to convey messages of liberation, full-development, and unfettered happiness."
https://en.wikipedia.org/wiki/Atheism
With the given that the term "or" in the above definition of mystic can mean a link to alternatives, we can remove 'Deity' from the definition.
So stipulated, can an atheist such as an axiological atheist or existential atheist be a mystic?
"I don't believe" the sun will rise does not cause the sun to not rise, any more than " I do believe" the sun will rise causes the sun to rise.
Nature is independent of " i believe I do not believe." Thus mystics are independent from "I believe I do not believe."
"I believe I do not believe" is a singular limited region of the brain throwing darts in the wrong direction. Socrates alludes to this in the shadows on the cave wall.