It may or may not be "large" depending on how it
was laid out; multifinger would be much, much
better than single stripe. It could be legal in any
case if "taps" were close-in, and if the foundry did
not assert W-limit rules to complement the limits
of model extraction geometries.
Issues about very wide single stripe devices include
debiasing and electromigration, and gate resistance.
Even if Rg is modeled (lump style) the distributed
nature of it will impact high frequency operation.
Maybe a "don't-care" for an op amp.
But I'd recommend making it multifinger in any case.