We need to look at what a “pay driver” actually is. In itself, the term pay driver refers to a driver to pays for their F1 seat either by his own posessions or by bringing sponsors. That definition matches Maldonado very much. While he has shown talent, his Venezuelan money is a major part in him having that seat.
Now we must enter lexical semantics, because the bigger question is the inherent negative connection of the term “pay driver”, mainly caused by questionable F1 careers such as Deletraz or Lavaggi (although they have shown at least a basic level of talent after their F1 career) and the lack of insight into F1 business at said time, causing a disregarding attitude for and/or lack of knowledge of more successful drives who had money involved.
To put it short: describing Maldonado as a “pay driver” is, from the mere literal meaning of the term, not incorrect. The inherent negative connection with pay drivers, however, may make describing him as such a bit unjust. So, if one is using “pay driver” as an insult to him, it is unfair. If it is merely used to describe facts, it’s acceptable.