No. Many of them are successful poets: Russell, C.L. Stevenson, Whitehead, Nietzsche, Marx, Hegel, Berkeley, ......
And for that matter, some very good poets could be considered failed philosophers: Yeats, Wordsworth, Blake, Rochester, Donne. . .
One can't limit "poem" to texts included on the Prelim Reading List of a doctoral program in English. One can read both Whitehead's Process and Reality and Russell's Human Knowledge as Comic Epics in prose, though they are at loggerheads philosophically. Both in their own way are marvelously written.
This suggests that I.A. Richards was on to something when he defined a book as a "machine to think with."
Carrol