The "delete" key can be configured to send one of two different characters. By default, the delete key sends a DEL (0x7f), which most devices expect. However, some devices expect a BS (0x08 or Ctrl-H). This can be configured under "Terminal" -> "Settings".
The "return" key can be configured to send a CR (0x0d or Ctrl-M), an LF (0x0a or Ctrl-J), or a CR + LF sequence. Most unix-based machines expect a single CR character, but some devices may expect an LF or a CRLF sequence.