I have no opinion, I have no experience with source estimated from ECoG data, you should rather contact the authors of these articles (@AnnalisaPascarella), or the OpenMEEG team (@Alexandre, @mclerc, @papadop). If they think it is correct to use the forward models computed for ECoG with OpenMEEG for minimum norm imaging in Brainstorm, then OK. But we won't be able to provide any help regarding the weird activations you observe away from your recording sites.
There are probably things you can try with your recordings before going for this advanced electromagnetic modelling methods.
About the tutorial, yes, I used the example dataset and followed exactly the tutorial. I have this error:
[process_epileptogenicity] Epilepsy > Epileptogenicity maps (A=Baseline,B=Seizure)
Line 37: fileparts (line37)
This bug is already fixed. Update Brainstorm and try again.