Please see my comment inline.
> More generally, in the case of a front-end nodes with a processors definitively different from
> worker nodes (same firm i.e.Intel) can openMPI applications compiled on one run correctly
> on the others?
It is possible to come up with a set of gcc flags that generate a "generic" binary for both systems. The problem is that the generic code would not be optimal for backend nodes. As a result it may effect on applications performance.
We had a similar setup issues on our platform as well. As a work around, we compiled two version of the code and merged them to single install directory.