No, controlling Logelloop with relative values is not possible.
But you can change the settings in Projet Edition/behaviour/Interface Options.
In this panel, you will find :
“Minimum value for midi speed controller” and “Maximum value for midi speed controller”
Set the values you need for mini and maxi and your midi controllers will have the behavior you need.
This is explained in the user manual at “Using MIDI to control the speed, pitch and time stretch.”
If you want specific settings for each track, you can do it using a macro to convert a MIDI controller value before sending it to a Logelloop button. I you need it, I can make a tutorial for this.