You can definitely flash foreign builds onto the XT1060 Dev Edition. I was in fact running the German build of 4.4.2 on my XT1060 because there is no bloat to mess with. I've switched to the T-Mo 4.4.2 build now so I can use faux kernel but thats beside the point. I have no problem using these builds on Verizon's network as long as I have LTE/CDMA selected as the network mode (instead of LTE/GSM).
BUT
You can only flash system, boot, and motoboot to my knowledge. I haven't flashed any of the others because I haven't wanted to take the chance and have to spend time fixing it if something goes wrong. If you know how to use fastboot to flash specific files then you're golden.
If you want to use your XT1060 on GSM networks, then flashing system, boot, and motoboot from a T-Mo or foreign build will help you in that department. The VZW firmware doesn't have a lot of options for GSM networks (network modes, APN settings etc.) but the GSM builds do.