Yes, we welcome applicants of every nationality. Keep two things separate:
Applying and attending Academy (a course)
Open to everyone. Attending a course is not work, so it needs no work permit, only the right to visit the country where the Academy runs. Depending on your nationality you may need a tourist or short-stay visa to enter; check that country's entry rules.
Working paid assignments (once approved)
Each country sets its own visa and work rules, so what applies depends on the destination and your nationality. As a general guide for most Mediterranean destinations (Croatia, Greece, Italy, Spain and France):
EU / EEA / Swiss citizens: can work and provide services with no work permit.
Non-EU citizens (including UK): need the appropriate work authorisation or a recognised exemption. A tourist or visa-free entry does not allow work, and the Schengen 90-days-in-180 period is for visiting, not working.
Outside the Mediterranean (for example the BVI, Thailand and Tahiti) each country has its own entry and work rules.
It is your responsibility to meet the entry, visa and work rules wherever you attend or work; we will help with guidance and documentation where we can.