10 kg extra is not a *S benefit. However, when I have checked in at OSL with my silver card flying lufthansa, it is the sas crew that does the check in, and they didn't seem aware that the 10kg doesn't count for LH. So i think it should be no problem. But I have no idea of how the checkin agents in MEL are trained, they might double check this and follow the fules strictly.
Only someone with good knowledge of TG's MEL checkin personell could say anything more certain about this.

The *S benefits:
http://www.staralliance.com/en/trave...er_status.html