No, it’s not okay: an application is not defined by a device type. Even a single customer should be able to define multiple applications using the very same device types. Also, this is not even a valid AppEUI, and who knows if Dragino or another manufacturer isn’t using the very same AppEUI for another device type. See my earlier answer above.
That said, it’s nice, and weird, that this works for some of you (at least with the current version of the TTN stack) while others needed to change the AppEUI to get things to work. I’d not risk having to fix this later though, and I’d give the devices a proper AppEUI before deploying them.
As for coverage: the activation method does not matter. if ABP works but OTAA does not, then such only implies that uplinks work but downlinks don’t, or not that well. In that case ADR would not work either (and you’d need to explicitly program basic network settings as well). Also, just to be sure you know: you should not do an OTAA join very often, and once joined there’s no difference between OTAA and ABP.
Maybe Gateway queries & ranges helps, but it’s a long read.