Yes, in custom loops this is the usual "modus operandi" in that Push/Pull is a very common. Be aware tho that the very evident noise from 2 fans will be noticeable increased with 4 unless you take steps to lower fan speeds. The extra fans will deliver a boost in thermal performance of between 10 and 30%, This increase tends to be greater at lower fan speeds (1200 rpm) and less at higher speeds 1800 rpm... with the H100is 2700 rpm, I dunno what you will see but I'm sure there's a youtuber who tested it,