I disabled dnsmasq, because I use PiHole as my DHCP and DNS Server. LEDE successfully got the DHCP lease and I can ping from LEDE other hostnames in my LAN. But when I use nlbwmon-luci-app the hosts just shows up as - (
). Is it possible to use the PiHole DNS Server to display the hosts?
Sure. If you have not specified a LAN DNS, specify the PiHole. That would likely fix your issue.
as you see the router can ping hostnames 
but nlbwmon doesnt use it.
I dont think I can specify the LAN DNS since the router is using DHCP. Or did you mean something other?
Anyone has an idea? Showing the hostnames would be very helpful.