Think what accessibility means: It's for people who visual or other handicaps. They can't read the text so they have to have a screen reader read the text to them. How could a bevel and emboss which they can't see be of any use.
If you must have that graphic appearance, then make it an image of the effect (with Photoshop or by rasterizing with Object Export Options), place it in InDesign, and add an Alt Tag so the screen reader will have something to read.
I don't need to "think" about accessibility and I know all about alt tags as I've been doing this for years. However, I've never used InDesign's bevel/emboss on an image before and therefore have never encountered this error. The PDF is for the consumption of everybody: disabled and non-disabled (the hosting site will only allow the uploading of one PDF, so variations cannot be created). I acknowledge that people with visual impairments will not be able to appreciate the effects, but non-disabled users will.
However, the use of Photoshop is a good workaround (presuming that will get through). Just don't why this particular effect in InDesign would make the image "inaccessible content".
I don't know either. It sounds like you do more work with accessible PDF than I do. Sorry if I was over explaining. It hard when answering a question to know where people are coming from, if you know what I mean.
No worries Steve. Thanks for taking the time to reply. Perhaps the lesson I've learned is to use an image-editing program like Photoshop rather then rely on InDesign, especially where accessible PDFs are concerned.