The phrase "it is skeptical" is grammatically correct and can be used in written English.
It typically means that something is doubtful or uncertain and expressing doubt or hesitation towards something. Example: "The results of the study are inconclusive, therefore it is skeptical whether the new treatment is effective."
For sure, it is skeptical about the consequences of the Avengers' actions.
It is skeptical of subtle arguments, wondering what they really mean.
It is skeptical of "the application of social science theories to real world problems" and cognizant of "human fallibility/corruptibility".
"The I.A.E.A. has been consistently telling journalists that it is skeptical about the Syrian nuclear story, but the reporters are so convinced".
The battle over the rules that determine the reach of the nation's largest media conglomerates moves early next year to a court that has already indicated that it is skeptical of further deregulation of the industry.
It is skeptical insofar as it denies that immoral actions are always irrational.
Theory was skeptical about meaning and objective value — hence about the very idea of a "great book". At its flamboyant worst it was skeptical about the very idea of rational discourse.
Some who have seen it are skeptical about its most advanced features and say it costs too much.
When intercepted German cables revealed the plan to Allied Intelligence, those who commented on it were skeptical of its feasibility, considering that it was beyond the German powers.
Mr. Wallach approached Advanced Micro Devices about partnering, but it was skeptical.
William E. Pelham, the director of the Center for Children and Families at Florida International University, which conducts research on the disorder and treats children who have it, was skeptical about the test.
