No, it’s not ok to not include dates on a resume. Employers need to know when you held each position and how long you held it to determine how much experience you have.
However, removing the exact months of employment from your resume’s work experience section is acceptable. If you have employment gaps this can be a good way to make them less apparent.
If you want to further downplay the dates on your resume, use a functional resume format. Functional resumes take the reader’s focus away from your chronological work history and instead highlight your professional skills and expertise.