If you were a dying race, and you had limited resources, and your ships were designed for elegance rather than slogging matches (like the IN), would you ram? I think the Eldar would run away, killing themselves in a ramming attack does seem a little unlike them. Even the shape of their vessels suggests ramming is not on th agenda, unlike with the IN and Chaos fleets were the prows are obviously designed to be able to ram (especially in the IN's case).
As for suicidal ships, I think in fleets such as the IN, suicidal ships are characterful. Its part of the human mentality of never backing down, stubborness in the face of adversity, etc, when in fact you'd be better off just escaping. Look at the German light cruisers at Jutland, they turned to ram the British dreadnoughts (before being ordered to turn away) to allow the German fleet to escape. It made little sense tactically (as it just left the light cruisers burning long before they could have reached the Brits), but thats the sort of crazy-brave thing people do. So yes, suicide ships should be rare in BFG, but they should be allowed for the 'human' races.