O artigo de referência (mencionado na parte inferior do artigo que você citou) declara e em O padrão de pool de conexões do IIS 4.0 e posterior está ativado. Então você não precisa ativá-lo através do registro.
De outro artigo :
To use connection pooling optimally, there are a couple of rules to live by. First, open the connection, do the work, and then close the connection. It's okay to open and close the connection multiple times on each request if you have to (optimally you apply Tip 1) rather than keeping the connection open and passing it around through different methods. Second, use the same connection string (and the same thread identity if you're using integrated authentication). If you don't use the same connection string, for example customizing the connection string based on the logged-in user, you won't get the same optimization value provided by connection pooling. And if you use integrated authentication while impersonating a large set of users, your pooling will also be much less effective.
Certificar-se de fechar a conexão e usar a mesma string de conexão novamente é a chave para o pool de conexões. O IIS armazenará em cache a conexão e a reutilizará (essencialmente).