Can I use "Teammates" if my Pokemon was KO'd due to Poison damage?
No, you cannot. You can only use Teammates if your Pokemon was KO'd *during* your opponent's last turn, but Poison damage takes place *in between* turns.
Source: Primal Clash FAQ (2015-02-05), TPCi Rules Team (2015-02-05)

Relevant cards

Note: All applicable cards may not be listed below.
XY5_141
XY5_160