Yes, mail continues to reach inmates in the SHU at federal facilities including Thomson USP. Federal SHU inmates receive mail five days a week, which means a magazine subscription will get through even during a period of segregation.
The SHU strips away most privileges, phone access is severely limited, visits may be suspended, and movement is essentially nonexistent. But mail keeps coming, and that makes it one of the most valuable lifelines available to someone in that situation. A magazine subscription arriving regularly gives your friend something to read, something to look forward to, and a mental escape from an environment that is deliberately designed to offer none.
Reading material matters more in the SHU than almost anywhere else in a facility. The isolation and monotony are the hardest parts of segregation, and having something to engage the mind makes a meaningful difference in how a person gets through it.
InmateAid carries magazine subscriptions and can set one up for your friend at Thomson. Choose something aligned with his interests, whether that is sports, news, fitness, science, or anything else, and get the subscription moving. The first issue will reach him through the facility's regular mail distribution and subsequent issues will keep arriving on schedule.
A letter through InmateAid alongside the subscription lets him know you are thinking about him and aware of what he is going through. In the SHU, that kind of contact from the outside carries more weight than it does anywhere else.