There's no allowances for the tropical druid like that, just the classic four season -- but that in itself is really interesting as a concept. As it is, it's really that the druid simply has stronger powers in one season as opposed to the others - in essence, a +4 to caster level in their favourite season, +2 to one of the "sidebar" seasons (like Autumn or Spring as to Summer, for example), and +0 in Winter. The fluff introduction indicates that the reason for the focus on the seasons springs (haha) out of a focus on the flora rather than the fauna of the world (i.e. why they don't get Wild Shape I'm guessing). But this isn't reflected in, say, being better at casting plant-ish spells like Entangle or Plant Growth, it is reflected in the strength of their casting in different seasons and that's it. The concept is not worked through in a lot of detail.
A bit of both, to be honest. Secret Shapeshifting Masters Of Society is a well-worn concept, but this one just had nothing out of the ordinary, it's just all "We as a race escaped our interplanar prison ages ago, spurned all our gods, and wormed our way to the top levels of your societies where we puppetmaster events for our own benefit. INT +2, CHA +2, -2 STR, your primary spellcasting stat counts as +2 for calculating bonus spells and caster level, Energy Resistance 5, LA +1, and hey, for some weird reason Endemics are rarely a PC race." In a genre where you're at least a Reptilian Overlord or from Beta Reticuli, this was just ... blah.