The Splitter is not the issue. Any 4-pin fan Splitter can be used with both 3-pin and 4-pin fans.
How the fan is controlled is set by the way the mobo header operates. The ONLY way to control a 3-pin fan's speed is by using Voltage Control Mode (aka DC Mode) at the header. The type of Splitter does not change that. NOTE that the number of pins on the mobo header does NOT tell you what you need to know. It is true that a 3-pin header can only operate in Voltage Control Mode. But many mobos today use only 4-pin fan headers. The confusion comes because the method they use for control can vary. Some use only PWM Mode (true 4-pin system design). Some use only Voltage Control Mode (ideal for 3-pin fans, but also can control 4-pin fans). Some...