The prime purpose of NATO is deterrence; no-one wants to be forced into a shooting war - hence I expect NATO to be very wary of accepting a member which may invoke article 5 pretty much the moment the accession ceremony is over.
The Ukraine would have a much easier time getting into NATO if relations with Russia were cordial; however, as the mere act of exercising their sovereignty to join an alliance of their choosing is sufficient to prevent cordial relations with Russia...
The problem, obviously, being that Russia is not content to be secure within its borders, but also desires to have a say in the affairs of neighbouring countries (Which, incidentally, makes these countries feel much less secure, hence making them more eager to join alliances to improve their lot, precisely the scenario Russia wishes to avoid.)
Sigh.
There is no point of deterrence when if Ukraine is gone, and you have Russian tanks in Vienna in one week, Munich the other, and the rest of Europe in a month.
Ukraine in comparison has a miserably weak military that is strongly outdated compared to Russia.
How much tanks does Germany have, and how much does Russia?
I will do Googling for you.
354 vs 12000
Russia's tank force biggest problem? Having more tanks than pilots.
Half of this tank fleet is in long term storage for this reason, and what's left half is in rather bad semi-written-off condition.
If we let Russians to regain their breathe, it would not take them long to restore them, and regain this enormous military asset.
Russia only has 3000 tanks in service. The rest are mothballed. That's not half, that's 75+%.
Even looking in total, the vast majority of these "12 000" tanks are in fact T-72s, 9000 of them. We already know how T-72s fare against modern tanks.
For sure, 3000 decent MBTs is a formidable force. But 3000 vs 1000 is not going to let Russia steamroll when their air force is set-up for defence and not offense. Even an advantage of 3:1 is not going to do you much good when your opponent has absolute air supremacy.
A Russian offensive into Western Europe will definitely get stalled, there is no question about it.
If relations with Russia were cordial, the Ukraine would have no need to get into NATO to begin with. In that ideal world, things would look different; we don't live in that world, sadly.