I would recommend that you see your surgeon immediately regarding your open incision. Having an open incision leaves your buttock at risk for infection.
Healing of buttocks incision
Your buttocks incision will heal with appropriate antibiotics guided by cultures as well as aggressive dressing changes.
I have found that a midline gluteal incision to be a highly effective incision. However, when it breaks down I would be concerned that there may be fluid collections (seroma) on one or both sides. An ultrasound would be a good way to evaluate if there is fluid collecting. When there is fluid collecting and it wants to get out, it will find it's way out through the incision which which cause the incision to start to break down.
Buttock implant incisiin healing?
I abandoned the single gluteal cleft (aka "butt crack") incision over 6 years ago because of a > 35% wound healing complication rate. Typically, the wound looks good for the first couple weeks before it starts to break down and eventually open up. From here wound care with dressing changes twice a day are required for a variable amount of time (>1 month most commonly). Hopefully the implant does not become exposed in this process, necessitating removal. Glad to help.