Yes, anything that doesn't expose your existence is safe. If you don't want to get banned, simply don't show your arse anywhere. And since dungeons have no ranking system, it's completely safe to push through. The devs can't just filter out everyone who've completely clear out dungeons and then ban them all, they need to carefully look at the list of thousands of players and selectively ban the suspiciously underpowered accounts, which is a total waste of work hour, so they'll never do it.
For example, I'm at stage 70-50 currently, but all of my dungeons are fully cleared, including guild dungeon. Buy my guild boss is at stage 42 only, I'm rank 15 in guild boss internally, rank 26k guild boss globally, but rank 2 guild member just because I got so many guild points from the guild dungeon maxed out, and I've been playing for months without any ban. Ofc I also take precautions by doing stage clear at around 11s to 12s, never going faster than that, as I've heard people like me who're playing super safe but got banned just because they online farm for 24hr at ~8s clear time. The devs still can easily filter out clear time from the pool of millions of players, and ban everyone who cleared stages at 8s, simply because it's impossible to do it legitimately without mod.