Celtic imitations of Alexander type tetradrachms: https://www.academia.edu/9763573/BI...ltic_Abstract_Iconic_Art_in_Thrace_3-1_c._BC_
Yes, indeed, and there are plenty of examples of imitation in ancient numismatics. However, some of the designs on Celtic coins are so highly stylized that they only hint at the devices they were modeled after. It's clear that in many cases, the engravers felt that our money needs to look like our money.
Indeed. Interesting that they managed to keep the core image/theme from the Hellenistic original, while still giving their versions a distinct 'Celtic' flavor...
