Are Bose Sleepbuds 2 safe?

Yes, the Sleepbuds 2 by Bose are designed to be safe for use while sleeping. They do not themselves physically contribute to any pain or strain on the ears while in use.

And with regards to the sound and volume they themselves emit, they were measured at their peak dBSPL at 74 dB which is below what would be needed for there to be permanent hearing damage.