Hi,
I can't really say anything on xbox, wii and ps publishing platforms as I never tried them nor heard about playmaker support on them, but I would not be surprised it's totally fine. Playmaker was in trouble with flash because it never got really ported properly by Unity to begin with I guess ( and they stop supporting it as a matter of fact...)
as for any third party system like Steam, this is totally fine, provided you can write scripts to work with their api. that's what I do on a daily bases, I write custom actions to enjoy working with playmaker AND other systems. So totally fine here. It does mean writing code tho, as playmaker can not support everything plugins and third party systems, that's unrealistic.
bye,
Jean