Yes, you can make an Old Fashioned with gin, actually any spirit you choose. The basic recipe for an Old Fashioned is a great way to play with different flavored bitters. This recipe works equally as well with either Lime Coriander or Orange Bitters.
2 oz gin
.5 oz simple syrup
4-6 dashes The Bitter Housewife Grapefruit Bitters
grapefruit twist to garnish
Combine gin, simple, and bitters in a mixing glass, add ice, and stir to chill. Strain into a tumbler with 1-3 large ice cubes. Garnish with a grapefruit twist.