In general (not considering the specific feat), I would say you are likely in cover from enemies at range as they are at an angle to the hole. If you're underground but the hole is really small, you might be in cover against someone above you. Though they would also be in cover from you.
If you are completely concealed underground and only sticking out a weapon to attack someone above, the might be Hidden to you and you to them.
Blind-fighting and tremorsense would give you an advantage here over a target that does not have these qualities.