Putin has a proxy - Belorussia, controlled by a same-type ageing dictator Lukashenko. He is doing a military mobilization right now and has borders with Poland and Baltic states.
Armenia is a member too, but Putin didn't help them in Nagorny Karabakh, saying it was Azerbaijan territory by international law. I beleive it was a demonstrative punishment for Armenian 2018 "velvet" revolution.
Kazakhstan is a member too. Putin used his army in Kazakhstan in January after Tokaev said that protesters are supposedly foreign terrorists.
Putin will not directly help Lukashenko against NATO countries on their territory, but is well capable of throwing his army to "protect" Belorussia from retaliation, including anti-air warfare.