Not licenced individuals cannot participate in any way in a Greek Law firm. Only Greek and EU/EEA nationals may qualify as lawyers.
"Article 6 - Legal requirements - Barriers
The lawyer must:
1 . Be a Greek citizen or a citizen of a member state of the European Union or of another state, which is a party to the Convention on the European Economic Area. A Greek can be appointed a lawyer with the permission of the Minister of Justice, which is issued after the opinion of the relevant bar association.
[...]
Article 49 - Establishment of a Law Firm - Headquarters Branches - Legal entity Company name
1 . A Civil Law Firm (hereinafter referred to as the "Law Firm" or the "Company") may be established only between practicing lawyers (hereinafter referred to as the "Partners") for the sole purpose of providing legal services (anywhere, inside or outside Greece) and the distribution exclusively between the Partners (according to the method, which they will agree at their non-binding judgment) of the total profits, which will result from the activity of the company. [...]" (Lawyers' Code (4194/2013), subsequently amended, Articles 6 and 49 [google translation based on unofficial text at kodiko.gr])
Lawyers' Code (4194/2013), subsequently amended, Articles 6 and 49
[<a href="http://www.et.gr/idocs-nph/search/pdfViewerForm.html?args=5C7QrtC22wEaosRGzKxO6XdtvSoClrL8A9d-yAUcKEJ5MXD0LzQTLWPU9yLzB8V68knBzLCmTXKaO6fpVZ6Lx9hLslJUqeiQZo6QYW-uV-ENHV699Y3tkm_Vc8nmsGuL9nO7gKwnjWc.">Code (official)</a>],[<a href="https://www.kodiko.gr/nomothesia/document/76222">Code (unofficial)</a>]