Here is an excerpt from a paper by Alice Turk, Professor of Linguistic Phonetics at Edinburgh University, concerning the phonology of flaps in American English:
Here we are concerned with examples like (2) above, where a /t/ occurs between two unstressed vowels. Turk's example, provocative, has the same morphology as the Original Poster's word relative. In both instances the /t/ is intervocalic (occurs between two vowels), and occurs between unstressed vowels.
As described by Alice Turk, the flapping of /t/ in this environment is optional. This is well-attested in the comments here, where several respondents point out either that this /t/ is flapped, or that it can be.
In short then, [ɹɛləɾɪv] doesn't sound odd at all. Whether an individual happens to flap a /t/ in this sort of environment will depend on many factors: the personal habits and predilections of the speaker, whether they are saying the word alone or in a sentence, the speed at which they are talking, and so on and so forth.
It may interest readers to know that several dictionaries give the transcription of relative with a flapped /t/. Here for example is the transcription from Cambridge Dictionaries:
relative
noun [ C ] UK /ˈrel.ə.tɪv/ US /ˈrel.ə.t̬ɪv/
That little upside-down hat under the 't' represents a flapped /t/. The audio here also uses a flapped /t/.
And here is the transcription from Oxford Dictionaries clearly indicating a flap for a /t/:
relative /ˈrɛlədɪv/
Note:
It has been suggested elsewhere here that the last syllable of relative has secondary stress. It doesn't, at least not in the normal meaning of the term. In words with secondary stress, it's possible to have a rhythmic stress on both stressed syllables:
- 'abso-'lutely fan-'tastic.
In the utterance above we can have a full stress on each of the three bolded syllables, including both the first and third syllable of absolutely. We cannot do this kind of thing with the last syllable of relative
- 'famous 'rela-'tive (stress on -tive, badly formed).