Can DCP-o-matic convert DCPs to something else (like TIFF or MP4)?

No. However, it's not too hard to do this from the command line. You will need FFmpeg which is packaged by most Linux distributions or downloadable for Windows or OS X.

FFmpeg can convert DCPs to almost anything. For example, to convert to a Prores MOV:

ffmpeg -i "some_video.mxf" -i "some_audio.mxf" -c:v prores -c:a copy "output.mov"

For more details on using FFmpeg with DCPs see Oliver Trenouth's page.

Unpacking

If you just want to unpack a DCP to its constituent JPEG2000 and audio files you can use asdcplib. A Windows build is available from here, or you can build on Linux with:

wget http://download.cinecert.com/asdcplib/asdcplib-2.5.11.tar.gz
tar xzf asdcplib-2.5.11.tar.gz
cd asdcplib-2.5.11
./configure
make
sudo make install

Then to extract the JPEG2000 frames from a video MXF:

asdcp-unwrap some_video.mxf

To extract WAV files from an audio MXF:

asdcp-unwrap some_audio.mxf