A screening is generally a much briefer and more superficial look at a person than an evaluation is. If you're paying for a report, it will be an evaluation, not just a screening. Often at places like early intervention centers, they have intake workers who do initial screenings, and only if the child appears impaired enough to that person does the child then get moved along to the next stage, where a full evaluation is done.
An OT with experience in sensory integration should be able to assess in various sensory areas (auditory, proprioceptive, vestibular ...), and may even be able to suggest that you have your child assessed further for possible ASD, but in my experience, OT's are not supposed to make that diagnosis and tend to be very careful about "suggesting" that a child has ASD - they are much more likely to recommend further evaluation. If, however, your child's primary ASD issues are sensory-related, getting this evaluation is a great start, and getting treatment in this area will help immensely.