I don't think its that risky at all.
Even with low big men skills, he can train them up really quickly because of his height. Worse case, you spend a season of training and you end up with a really well rounded player. And next season you can really start hammering his inside skills. He'll be a season behind when it comes to big man skills but it works out in the end cause other people going to slow down to train guard skills later on as well when you can just continue pounding the big men skills.
Personally I'd rather this sort of player then a C/PF with low secondaries. At least this case you don't have to really worry about training secondaries later on