Having an IEP for one service does not automatically make a child eligible for other services. Prior to the IEP, the school is supposed to do a comprehensive evaluation of ALL areas of suspected disability. Qualification for specific services is based on that evaluation, although the school may be willing to accept an outside (private) evaluation in place of doing their own.
So the school will have to either conduct an OT eval or accept your DS' s private eval. Similarly, if you want services to work on social skills and/or emotional regulation, he would have to be evaluated in those areas as well. You may need to request these evaluations in writing. You should have been given your State's publication about your rights under IDEA (special education law). The booklet should explain the procedure for evaluations and determining eligibility.
My son has autism and mild visual impairments. He gets speech, OT, APE, placement in special classroom, and other accommodations and modifications to his curriculum. At his most recent triennial re-eval, the OT tried to dismiss him from her services. None of his other services or accommodations were questioned, but I had to fight to keep OT services. DS's handwriting (printing and cursive) is like that of a much younger child, he doesn't have the fine motor skills to open food wrappers, and he can't work the fly on his pants. I was shocked that the OT thought it was appropriate to discontinue services. I had to request specific testing and then he qualified only on the basis of specific subtests. And I had to fight to have the decision made due to the subtest scores instead of the composite score.
So no, in my experience having an IEP for speech will not automatically get you OT.
Gena
DS, age 11 and always amazing
“Autistics are the ultimate square pegs, and the problem with pounding a square peg into a round hole is not that the hammering is hard work. It's that you're destroying the peg." - Paul Collins, Not Even Wrong