Yes, the monthly payment plan grants the same license as the single payment plan after 12 consecutive monthly payments.
Unlike the single payment plan, the monthly payment plan automatically renews and continues until the user cancels it. Should it be cancelled, it may be started up at any time. When restarted, any updates or additional content is included unless the content was exclusive to the month it was added. Cakewalk has not added exclusive content in some time.
One other thing about the monthly payment plan; once renewed, in order to keep the updates 12 consecutive payments must be completed, just like the original purchase. IOW, SONAR is not sold by the month.