at our shop, we use a lot of LINQ; generally, the developers write whatever they want, and if they hit a performance block, then that call gets modified to use a stored procedure; i'll write the stored procedure for them, and add/modify any indexes that might be appropriate to support it.

that resolves the performance issue for them.

I'm usually the one who identifies the slow queries and bring them to the developers attention;

i find out they are slow because they show up in an extended events trace for slow queries i capture on the production server.

generally, i'd say i do a couple of conversions like that a month.

I treat it as a support issue; i certainly would not think about drawing a line as the DBA Nazi and say "No LINQ For You!'