Poland could very well be a NATO member. The Russians will throw a hissy-fit, talk smack in the international press, decry Western hegemony in Eastern Europe to the UN, but they won’t go much beyond diplomatic and informational means to stop it, they may even go economic with the pipeline, but I doubt it. Ukraine is a different story. Ukraine will not become a member of NATO. Europe relies too heavily on the Russian and Azerbaijani pipelines for their oil and natural gas. Russia can cut off their supply of the former and destabilize the latter enough to where the flow is interrupted (they already have Armenia in their pocket and Georgia is obviously quite vulnerable to them as well). This would sink Europe. Their governments won’t allow it, not in a million years.
Poland has been a full member of NATO since 1999. Your opinion of their status is irrelevant.