Dez, if the silencer is smaller or more restrictive, then it will affect power and possibly engine life.
Remember the problems associated with the AAEN spark arrestor?
http://www.suzukiquadracerhq.com/lt500r-exhaust/dr-q-v2-0-pipe-and-2-0-engine/?message=4515

Only way to know for sure is to find out what the measurements and such are on the RM250.
If it's less restrictive, go for it.