Sure you can add multiple consumers to the same channel, like so:
<channel>
<video-mode>1080i5000</video-mode>
<straight-alpha-output>false</straight-alpha-output>
<consumers>
<decklink>
<device>1</device>
<embedded-audio>true</embedded-audio>
<channel-layout>stereo</channel-layout>
<latency>normal</latency>
<keyer>external</keyer>
<key-only>false</key-only>
<buffer-depth>3</buffer-depth>
<custom-allocator>true</custom-allocator>
</decklink>
<screen>
<device>1</device>
<aspect-ratio>default</aspect-ratio>
<stretch>fill</stretch>
<windowed>true</windowed>
<key-only>false</key-only>
<auto-deinterlace>true</auto-deinterlace>
<vsync>false</vsync>
<borderless>false</borderless>
</screen>
</consumers>
</channel>