Ive found it fine. The glute area is reasonably large. But I mean unless youre subq'ing 10ml of oil where theres a high risk of lots of seepage, I hardly see it being an issue of proximity. And no-one is subq'ing 10ml of oil, obviously.
The more relevant concern would be frequency, not proximity. As in, scar tissue risk if youre pinning 4 sites on an ed or eod rotation.