Probably not, the US skirts the legal definition of a blockade by creating insane hoops to jump through. Countries that want to trade with Cuba can’t use the SWIFT banking system, meaning no digital transactions, meaning they literally have to carry the cash with them to the island and back. They have to use ships that can’t dock in US ports for 6 months after docking in Cuba (which Cuba having a gdp less than half a percent of US gdp means businesses have no incentive to choose trade with Cuba). And the trade has to be humanitarian, no military applications (but this also applies to medical and tech equipment which US says have “dual purpose”). All that said, there are awesome countries that choose to go through these hoops at significant cost and risk. But it takes a lot of time and planning to setup and get the right permits.
Can’t find much about the numbers of prisoners. But folks should check out the plan progressivo. (i had to use scihub to view) Most Cuban prisoners have short term stays (1-4 years). Are paid the same as civilians. Are watched and given political education by civilians who do the same work, live in the same quarters and eat the same food as the prisoners. There are lots of sports, with baseball being pretty popular. It kinda sounds closer to a summer camp with classes, paid farm work and camp counselors than what we think about prisons in the US.