Lucky you not having winters, you should be fine then. The recycled numbers you refer to are 2 which is HDPE and 5 which is Polypropylene and yes both of these polymers are safe for your use. The only slight concern i'd have if you live in a very hot country is the long term effect that the suns UV rays may have on the polymer. UV rays, over many years, can make plastic degrade and become brittle. Plastics that are meant for outside use are usually UV stabilised. If the manufacturers made these with a view to inside use then i doubt very much they are UV stabilised.
In any case it would probably take many many hot summers of the sun beating down on your tub for it to begin to degrade. That said though if you are sinking your tub in the ground then that would be the ideal solution.