Has anybody installed MikroTik RouterOS v4.4 on DL360 G6 server?
No experience sorry but given 4.4 runs on a fairly basic 2.6 linux kernel I wouldn't worry too much. You certainly won't run into any CPU, memory or BIOS issues, the worst problems you might have to get around is finding a disk controller driver depending on which model you have and potentially a NIC driver, but the latter is less likely as they tend to use fairly common chipsets.
So no experience sorry but hopefully some encouragement to get on with it and try! :)