Splitting Sensor Signal

Am I going to be ok splitting a sensor signal if both receiving units use the same main ground?

Generally yes, but this only works for signals fed to "high impedance" inputs on the receiving devices. This won't work for 2-wire variable resistance sensors (ie, temp sensors) which typically have a pull-up resistor within the receiving device to create a voltage divider.

We are often able to share TPS and MAP sensor voltage between an ECU and a Logger.

Why don't you tell us more about exactly what you are trying to do? What sensor, ECU/Logger brand/model, etc?

I've got an AEM logger and a Stack Dash on a 1970 mustang that I'm wiring from scratch. The dash needs sensor data to display it and I need the same data to log it.

So basically all sensors on a carb engine with no ECU to control it. Mind you that's just oil temp/pressure, water temp. The other things that will be spliced will be rpm signal, fuel level and speed sensor signal which is a hall effect on one wheel.