A good test of whether a word is acceptable to use as an adjective is modification by degree modifiers like pretty, very, rather. There are some relatively recent examples to be found of confronting being used in this manner.
The biggest influence on my work and my way of looking at the world has
been psychotherapy. It's a very confronting business. # MA
Craziness is terrifying. It almost seems to be the thing that it's
here for -- to be frightening and to make no sense. The things that
make no sense are frightening. (MAG: New Statesman 10/10/2014, “We are
heading for a wilderness”)
We're just having games, playing. Playing, and being recorded. It's
very confronting, not to know the lines and have to go to that
place. I was hoping you'd be comfortable to jump up and give it a go.
(Aim High in Creation, Year: 2013 / Genre: Documentary, Adventure,
Comedy)
I imagine it must have been an agony for her family to experience it
privately, without having to endure it publicly as well. Having said
that, going through this collectively was probably very confronting in
a society that is fixated on superficialities, youth, and beauty.
(BLOG )
Mack, 26, said in an exclusive interview. " I'm sure it will be very
confronting because I think of her every day and deeply regret what
happened. " (NY Post, `Suitcase Killer' Heather Mack remorseful
after release from Bali prison)
There's a lot of hits for 'very confronting' in the news especially, though most seem to be in quotes from interviews like the last example above.
The Oxford English Dictionary does have an adjective listing for confronting. However, their examples are all rather dated and could also be analyzed as verb uses.
1614 W. Raleigh Hist. World i. i. x. §3. 191 The confronting, and
next people of all other vnto it.
1710 E. Ward Vulgus Britannicus: 3rd Pt. 115 Large Confronting
Bumpers pass.
1798 J. Hucks Poems 178 Ev'n now confronting armies meet.
The Cambridge Online Dictionary entry seems to fit what you're looking for.
adjective mainly Australian English
causing strong or difficult feelings, especially in a way that creates
thought or discussion:
I found her talk very engaging and at times confronting.
More examples
I can understand why people found parts of the film confronting.
Without these women even opening their mouths they've already been labelled as "absurd", "confronting", "frightening", just because of
how they dress.
He states that many Aussies tend to find differences in other cultures "confronting" and can't be bothered to see things from any
other perspective.
He likes the word "confronting", as in, "intimacy can be really confronting for people".
Her art is utterly contemporary, sometimes confronting.