A great deal depends on the relationship between the various symptoms you have and the Arnold-Chiari Malformation Type I which you have. If the symptoms are arising directly from the malformation it is highly likely that acupuncture might have minimal effect other than perhaps to reduce their severity. As you will see from the factsheets of evidence here for vertigo and headaches, there is a gathering body of evidence that acupuncture may be of value.
Tinnitus is a different matter. Although the factsheet here offers a small hope the reality is that tinnitus can be one of the most intractable problems to address, with many people investing huge amounts of time and money to no avail and then experiencing a total loss of symptom for no apparent reason.
Given the specific nature of the malformation you have, however, if you did decide to have acupuncture treatment your practitioner would benefit greatly from talking to your consultant(s) to detemine how much of your symptom pattern derived directly from the physical fault, and how much might simply be contingent. This would enable them to give a much clearer answer to how much they think they might be able to help you.