Combine the port, juices, and garlic in a nonreactive saucepan. Bring to a boil and simmer until reduced to 1/3 cup. Put the shallots in a stainless bowl, strain the reduction over them, and cool. Add the egg yolk, port reduction, and red wine vinegar to a bowl and whisk to combine. Combine the safflower and walnut oils and drizzle into the yolk mixture, whisking to emulsify. Season with salt and pepper.
Dress the romaine with the pomegranate-port vinaigrette and season with salt and pepper. Divide between 8 chilled plates. Divide the grapefruit segments between the salads. Sprinkle crumbled Roquefort, then walnuts, and finally pomegranate seeds on top of the salads. Serve immediately.
Consumption of raw or undercooked eggs, shellfish and meat may increase the risk of foodborne illness.