is it safe for a dog to have olive oil? say a teaspoon full on each meal. would it benefit the coat?

Safe, yes i suppose so, but not really necassary long term.
If the dog is on a decent feeding regime it'll get all the EFAs it needs anyway.
If you want to add more omega 3 and 6, it's much better to give the dog a few tins of oily fish 2-3 times a week.

Olive oil will not provide a good source of Omega 3 (omega 6 and 9 are already plentiful in food), better to give fish body oil which will also have the benefit of DHA and EPA

Is this the Salmon oil or similar?

I've had it suggested to supplement my girl with some omega 3 as she's just developed the tiniest hint of a heart murmur - would some tinned sardines be ok? More fun for her than just buying tablets! How many and how often for a Cavalier please?

(sorry for slight hijack!)

salmon oil, or FBO capsules eg from Healthspan. and yes you can give tinned sardines/pilchards/mackeral