I teach both flute and piano, but am also a freelance performer on both instruments. Virtually all my work as a pianist is as an accompanist, official accompanist for various schools, competitions, festivals etc. So it goes without saying that I always play for my own students at all levels, and make sure they are entered at a centre putting on exam visits where I am official accompanist so I know I will be free, as it's a pain having to be free to go to a centre for just one or two exams.
One major change in the approaches of music colleges is that they used to insist that students did second study piano. Now they largely discourage this, as the focus for most has to be just the principal study. This kind of focus has led to far more instrumental teachers out there who have little piano skill, or who have more than they let on, but feel ashamed to use it even in front of their students, so they never accompany their students, so students don't get used to playing with a pianist in the early years.
Even when accompanying early grades, I quite frequently find they come to their rehearsal with me having never heard the piano part, and often surprised that there even is a piano part! On occasions where using an accompanist is advised but not compulsory and an accompanist is provided, like masterclasses or competitions, I am more frequently finding students turning up to play music that should be accompanied but opting to play it unaccompanied. Clearly they simply view piano accompaniment as an inconvenient and perhaps intimidating distraction. Obviously I find this very sad as someone who has devoted much of my career to collaborative piano playing, and view music as an experience to share.
So while it is totally reasonable and sensible that teachers should only accompany their students in exams if they fee assured and comfortable doing so, and for many that will mean early grades only, and others not at all, I would always say that as long as teachers have access to a piano in their teaching room and at least sufficient basic piano skills, it is of huge benefit to their students if they do what accompanying they can from time to time in lessons, particularly in the early years. Students are far too worried about themselves to judge their teacher's piano skill, or even notice if it's not very accurate!