The plate armour was combined with traditional (read: pre-Western contact) Japanese armour styles to better protect the wearer from musket balls and other various related firings. I talk about armour development in Japan here, with this relevant line:

Their armour was more to deal with arrows loosed from bows and spears, and later on against musket balls, [...] It's worth noting that, upon contact with the west and the advent and adoption of firearms, [Japanese] smiths developed armour to better stop musket balls. A good idea of how this was implemented is seen in nanban gusoku ^[link], where you can see how a combination of the strong metal plate seen in Western armour is integrated with more traditional style armouring in the limb guards.

So yes, some did wear this plate armour - as to their effectiveness, it depends on what you're comparing it to. To prior-Western contact armours, or against what weaponry, for example.

Plate armors were used in battle after contact with the Portuguese in 1543. Sometimes, European cuirasses were imported or manufactured in the same style and combined with more traditional arms. The Japanese also designed some native plate armor (cuirasses) and helmets, such as the yukinoshita style cuirass, and zunari style helmet.

I'm not entirely sure if this could be considered plate armor or not, but also common was cuirasses of iron bands riveted together. Either way, this style of armor was still able to stop musket balls like (other?) plate armors could.

These armors became common among Samurai by the end of the Sengoku Jidai.

Plate armors were adopted by the Japanese because they were more effective. While lamellar is good protection against arrows and spears, it can easily be penetrated by arquebus fire. Meanwhile, plate armors can resist arquebus balls, and some cuirasses and helmets were tested for their resistance against arquebus balls. With the advent of the arquebus in Japan in 1543, one could see why the Japanese would also adopt plate armor.