What model server specifically? Usually only the 1U servers ever came with 2x 3.5" drives. The 2U servers often had 6x 3.5" drives. It's possible but will depend on which server specifically and whether they even offered a 2.5" drive option on it.
From what I can dig up on the R300, it was offered in 2x 3.5" version only and possibly not even hot-swap (hot-swap was an option). A newer R410 has the option of 2.5" drives but it's an 11th gen server, yours is 10th gen so I don't know whether the components would be compatible.