Currently there is no 64-bit agent for Endpoint as far as I know, trying to get the offical word but as far as i understand on the endpoint side it is 32-bit only. Will double check that
Also there is not a supported agent for mobile devices, yet I have heard that it is on the roadmap.
For data rest it does not matter whether or not the server is 64-bit or 32-bit as you doing the scanning against the file share/database/etc...
A lot of the performance issues/throughputs/latency all depend on how you set things up and also what product within DLP you are talking about as well (Data in Motion vs Data at Rest).
Each DAR scan can be throttled and scheduled around backup windows, work hours, etc.
Drop me a note if you have further questions or would like to talk in person