I was told by my dealer that the CRF250L and CBR250R use the same engine therefore I can safely order accessories that are available for the CBR250R engine for use on my CRF250L. Is this true?

The answer is Yes and No, the Honda CBR250R and Honda CRF250L engine are very similar and they share many parts together. But some parts are completely different, take the clutch plates pack which has for the CRF250L a few extra plates, because of this a few other parts are different.

Also the fuel lines for a Honda CBR250R are not suitable for the Honda CRF250L, this because the CRF250L uses more than 100kPa more fuel pressure in the fuel-injection system. Not directly related to the engine, but that also means that the fuel-pump is different. For the fueling, the Honda CBR250R uses a 38m throttle body while the Honda CRF250L uses a 36mm throttle body.

They have more small differences, so it's safe to say that you should check with the accessory supplier if the product you want to buy is also compatible with the Honda CRF250L.

Speaking of CRFs; some guys in Chiang Mai are reporting failed clutches on their CRFs.
RideAsia.net has examples.