I think it depends, they are not there all the time. For sure I saw none when I was there last summer.
From the hotels perspective there is no point freaking people out with talk of sea urchins when they are not there. I presume whenever they appear, the staff whip out the free sea-shoes at the beach shack
No - when I was there I was warned, shown pictures and advised not to go in the water - but no shoes offered (this was Nov last year)