I suspect you will need new ones. Not the Acorn style, rather the open top type.
I think the wall of the steelies is thinner, and the lug will bottom in the acorn style lugnut before reaching proper torque.
That's what I did with mine.
(Now that I think about it, I think my set came with the alternate lugnuts...)
When installing, be super careful to bring the nuts down by hand evenly so the wheels center up properly. Then tighten with the proper torquing pattern. Universal steelies locate on the lugs, rather than the hub like the factory alloys. Failure to center properly will give you a nasty vibration.
Generally speaking, they should work. Why would I think this?
Because the chamfered style lug nut is what you'd need to use with the spare tire wheel....unless your car came OE with a 5th alloy wheel for a spare.
The acorn style should have enough depth to tighten on the spare. If not, everyone that has alloys wheels using acorn style lug nuts and a steel wheel for a spare will need to carry extra lug nuts.
The good thing about the tire rack steelies is they are hub centering.
I *think* on my LL bean alloys I saw a small angle difference of the tire-rack nuts (in use by my some at the moment) vs the outback nuts.
I compared his 06 forester alloy lug nuts to the tire-rack nuts I put on his car (he's remote so I can't monitor for issues), and the angle was the same, no question.
I did see the tire-rack nuts have a little bit more available contact area on the angle portion, and the matching area on the steelies seems to also have more contact area.
The subaru acorn nuts seem to be the same size from our cars with steel wheels and alloys, but if the nuts do seat a little deeper into the tire rack steelies that could be where concerns about bottoming come from.
On all our cars, 03 OBW, 06 OBW, 05 forester, 06 forester, the open ended lugs all stayed a bit recessed in the end of the lug, all to about the same point.
I decided to get some lug nuts solely so there would be more 'taper' seated in the steel wheel, which the tire rack steelies seem to be designed for.
The lug nuts supplied by tire rack are called 'open end bulge acorn' or some combination of those terms, 'bulge' referring to the fact the tapered part towards the wheel bulges out further than the other parts of the lug nut.