Hi 
KNX uses 0…255 as well. “percentage” would be an invalid type for knx-expose - you can use “percent” if you have 0-100 values (even a string) or “percentU8” if you have 0-255 int values.
Same the other way around. If you get a raw payload from knx “100” it would not mean 100% - if you use a sensor with type “percent” you would get a 0-100 value.
There are some forum posts about using DPT3 and keeping state synced.
You may find some answers here: KNX Cookbook