Split valuation doesn't depend on Unit of measure..
Valuation type is not dependent on unit of measure..
If you create different valuation type for different UoM, then you have to be careful for that user use only the same UoM as per valuation type.
Suppose you have create 3 valuation type
1. KG
2. Ltr
3. ml.
And you have used UoM for material is 3.
1. KG
2. Ltr
3. ml.
Now user can easily use Ltr for valuation type KG.
In that case,
Use var. UOn as 2. So that user can use different unit during PO creation.
Guide your user to use valuation type same as order unit..
Then you can valuate material with regards to unit of measure..
Regards