As the privites Keys are yours and they are on your computer used to access the remote server, why not? ( you dont send your keys over the network)
So, if you have a full client then you see the whole blockchain and can harvest locally.
If you have a lightweight client then you don't see the whole blockchain and can harvest only by signing data received from remote server(s).
And now imagine that network is sybil-attacked and the attacker can trick you into harvesting on a fork...
easy fix, allow ncc to query multiple nis to ensure that the server your are harvesting on is not on a fork. eigentrust could also play a part but im not sure exactly how it works. from my minimal understanding of it, possible eigentrust could effectively blacklist the node with bad data and stop you from harvesting on it. idk, just thinking that could be a possibility to prevent that.