For symbols to work, they need to be understood. Think of symbols as a language; if you speak the language, and the readers speak the same language, everything's good. If, however, you speak the language, but the readers don't, your message would get lost, just as if you'd chosen to write half your poem in Ancient Greek.
The trouble with your example is, exactly as @Jay says, that modern readers are extremely unlikely to associate grasshoppers with Eos. Even for readers who are familiar with that particular symbol, this would not be their first association.
There are other ways in which you can use the same symbols, without losing the readers. For example, I could write about
Eos's green fiddler
Even a reader who is unfamiliar with the particular association, is likely to recognise the grasshopper, especially if you give a few more lines in the same vein. Here' the reference to the goddess is explicit, the fact that you are in fact speaking in metaphor is explicit, and it remains to riddle out only what could be a green "fiddler" associated with the dawn. Not too complicated.
If it is the god you wish to describe through metaphor, making use of their symbols, you'd need to use symbols the reader is familiar with. If your poem is a stand-alone, rather than a part of a larger work set in a particular mythology, you'd need to provide the reader with enough information to figure out which mythology you're talking about in the first place. For example, "lord of thunder" can be quite a few different guys. "Hammer-wielding lord of thunder" is Thor.
Note also that your bit of verse is quite wrong in terms of how the grasshopper is associated with Eos. Grasshoppers do not appear out of the ocean. They welcome the rising sun with their "song", thus they are considered the dawn's companions. They are not the dawn herself. If you're using symbols to convey a meaning, you must use them correctly. If you say 'chair' when you mean 'table', you shouldn't be surprised that what you're saying stops making sense.