There seems to be some general confusion about the pronunciation of the Roosevelts' name, even within the FDR article.  I've tried to find a few reliable sources for this info.

M-W gives:
Main Entry:
    Roo·se·velt
Pronunciation:
    \ˈrō-zə-vəlt (Roosevelts' usual pron.), -ˌvelt also ˈrü-\
Dictionary.com gives:
Roo·se·velt  /ˈroʊzəˌvɛlt, -vəlt, ˈroʊzvɛlt, -vəlt; spelling pron. ˈruzəˌvɛlt/
Inogolo gives this about Teddy's name:
Name: Roosevelt  Phonetic Pronunciation: ROAZ-uh-velt
Notes: There has been much debate about the correct pronunciation of Roosevelt's last name, however, in several letters Theodore Roosevelt himself specifies the correct pronunciation. In a letter to the Rev. William W. Moir dated October 10, 1898 he writes:
As for my name, it is pronounced as if it was spelled "Rosavelt." That is in three syllables. The first syllable as if it was "Rose."
Note that none of these sources make a distinction between Teddy and FDR, despite the claims of some that they preferred different pronunciations.  At the very least, each article should be internally consistent.  For Teddy, it seems to be clear that it's /ˈɹoʊzəvɛlt/.  His statement above makes that pretty clear.  FDR's case doesn't seem to be as unequivocal, but the same pronunciation seems to be the preferred one in most media.  The most common variant seems to be the barely noticeably different /ˈɹoʊzəvəlt/.  Most seem to cite the preferred pronunciation of the name being three syllables, not two.