Yes, it is most likely that kneazles were allowed inside Hogwarts. It is not certain if kneazles were allowed at Hogwarts as pets of students. Firstly, kneazles were not very common pets which may be a reason for us not hearing about a kneazle pet at Hogwarts. However, part-kneazles were allowed as pets in Hogwarts, as is evident from Crookshanks, who was part-kneazle and was allowed into Hogwarts as Hermione's pet.