I think so, from all the episodes so far, they’ve always mentioned him evading custom duty payable to the authorities and so he bribes the customs officers to release his diamonds, obviously saving him tens of millions. I think most diamond/gold merchants in this world evade tax one way or the other through offshore companies and all sorts of methods.
I don’t think they’ve ever mentioned him engaging in other illegal activities other than tax evasion. Ved engaged in drugs smuggling hence arrested.