Can poems and poetry be used interchangeably, or is that incorrect usage? In normal conversation, they are used as synonyms often.
Poetry refers to the art form itself. Poems means multiple instances of that art form.
Their use can overlap, but there are some instances when only one is appropriate.
This means that the art form is difficult to master, i.e., that it is hard to write poetry.
This means that the poems under discussion are hard to understand.
Here, though, they are essentially interchangeable:
My advice would be to use the word poetry when speaking about the art itself, and poems when you have a specific set of poems in mind. This will avoid any confusion.
It depends somewhat on the context; poetry can mean one or more poems, but in more figurative usages such as poetry in motion, meaning something outstanding or beautiful about a bird in flight, or a motorcycle race (as your tastes dictate), one wouldn't replace that with poems in motion, which would sound ridiculous.