If you are not comfortable working the glutes, just make sure you know of someone who is, in case you ever need to refer a client out for more specific work or if you are unable to resolve a lower back issue, piriformis issue or some other issue that is arising from this region.
Personally I work most of the glutes above the sheet/blanket, because I can get in deeper for the way I work. However, I am not opposed to working the glutes undraped – it is just that I generally only do this when I am working swedish style (using the glute work to blend into my lower back work) or with moderate to deep strokes which are very long in nature (from the ankle to the glutes, up the back to the shoulder and then on down the arm to end at the fingers).
I drape (or undrape the glutes) for comfort of the client and for whatever technique I need to be performing. I regularly need to get enough traction/shear on the sacrum/sacro-iliac region and use the drape as an adjunct, instead of using a skin on skin contact. I also occasionally use the drape to get a better contact with the ankles/lower third of the lower leg, when I don’t want to slide around on them or want to do a linear traction pull of the leg.
I can keep an entire glute and upper 1/3 of the thigh loosely draped while still working the length of the body under the drape, skin on skin, and never once have an issue with bunching or client comfort problems. I can also drape down to a lomi-lomi style if I like and still work the length of the body, it just depends on the client and what I want to do.
I was taught and look at the leg in this manner:
Put your finger on your belly button and then think of the leg as an extension downward from that point. Don’t think of leg and buttocks. Although the buttocks have specific muscles within that area, they provide a function within the leg apparatus itself, which can of course extend into lower back issues.
When you think about it this way (if you weren’t taught that), you can see how the buttocks become less of a point to be concerned about when a therapist exposes the area.
The black lines to the left demarcate what I am trying to explain in words.
Additionally, if you are a client who wants their glutes worked in a swedish style, and take your underwear off without talking to your therapist — you may not get what you are hoping for, depending on how your therapists works. He/She may just think you are taking your underwear off to be more comfortable and less restricted (many clients do this), not that you are actually wanting a specific type of glute work. Please remember to talk to your therapist about what you are looking for in your massage and be flexible if they are unable to provide you with what you are asking for. Each therapist works differently and has different training and/or levels of comfort.