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My 1995 Suzuki Escudo/Vitara 2.0 V6 (130,000kms) has started to smoke a bit, I’m told it is likely to be blocked oil baffles in the rocker cover (which I’m told is a common problem with this model). The options I have been given are to do an engine flush and see if blockage is cleared. Change over to diesel oil for next 2,000kms and hopefully the extra detergent in this oil will dissolve the blockage. Other option is to remove the rocker cover and clean it out – apparently a bigger job than it sounds and mechanic recommended I try one of the other options first. What option would you take? I am unfamiliar with flushing process but have heard horror stories of this causing more issues down the line. I plan on keeping this vehicle for the long term and do not want to cause unnecessary damage. Your advice would be greatly appreciated.

Engine flushing is fine if the engine isn't "sludged". This term refers to the oil throughout the engine becoming contaminated with carbon deposits and sticking to internal engine component surfaces, becoming as hard as concrete. Basically, an engine that is badly sludged is usually the result of a lack of servicing, a problem that has been associated with some Japanese Imports. When an engine gets to this stage, the only real fix is to completely dismantle the engine and thoroughly clean all the deposits, but as you can appreciate, this is not an economically viable thing to do on a 20 year old vehicle.
The horror stories you've heard about flushing are when the sludged deposits are flushed loose, going through the oil galeries and rapidly wearing the engine (like grit mixing with the oil). So it's not the flushing process which causes the problem - that was a pre-existing problem which the flushing process found out. A sludged engine will eventually fail by itself, without flushing - just that it may last a little longer.
So, to answer your question, flushing the engine and running diesel oil for a period could be a good solution, and probably worth a try, but if the engine is badly sludged, it may cause problems sooner than if left alone.

Thanks for your help with that. One further question - if I do put diesel oil in does it need to be the same ratings as the recommended petrol oil eg 5W-30 for this car or just a cheap diesel oil seeing as it is only for a short period?

I suspect you already know what my answer to this will be :)
It is always best to use the correct grade of oil as recommended by the manufacturer. However, according to data I have available, the 2.0 litre V6 Vitara/Escudo engine is designed to use 10w 40.