Safari 3.1 and nightlies of the same era do not report the same support for SVG as earlier versions. This is fixed in r6581, targeted for OpenLayers 2.6.

To fix this in your application, after OpenLayers is loaded, and before you create a vector layer, include the following code:

OpenLayers.Renderer.SVG.prototype.supported = function() {
        var svgFeature = "http://www.w3.org/TR/SVG11/feature#";
        return (document.implementation &&
           (document.implementation.hasFeature("org.w3c.svg", "1.0") ||
            document.implementation.hasFeature(svgFeature + "SVG", "1.1") ||
            document.implementation.hasFeature(svgFeature + "BasicStructure", "1.1") ));
};