* Hellenic as a synonym for "Greek": Yes, in this context, "Hellenic" encompasses all dialects of the Greek language, including Ancient Greek, Modern Greek, and all regional dialects.
* Hellenic as a specific historical period: This is where it gets more complicated. "Hellenic" can refer to the historical period of Ancient Greece (roughly 8th century BC to 146 BC), a time when the Greek language was more unified than it is today. However, even during this time, there were regional variations in the language, known as dialects.
Therefore, whether "Hellenic" includes Greek dialects depends on the specific context and how you define the term. If you're talking about the Greek language in general, then "Hellenic" includes all dialects. But if you're referring to a specific historical period, "Hellenic" might encompass only the major dialects of that era.
It's always good to be aware of the context and to clarify your meaning when using the term "Hellenic."