Is extra time on the GRE looked down upon?
ETS used to "flag" the scores of anyone who took the GRE under what they referred to as "non-standard test conditions". After an Americans With Disabilities Act lawsuit they settled and agreed to no longer flag scores, and according to their website:


  I heard that ETS is no longer flagging test scores that are reported to score recipients. Is this true?
  
  ETS has discontinued flagging almost all scores for tests that are
  taken with accommodations. For example, if a test taker receives
  additional time or extra breaks, the score will no longer be flagged
  in the report. In rare instances, ETS will flag the score report as a
  "nonstandard administration" only if the test is significantly
  altered.


This is true for other related tests, such as the GMAT. Note that this last line about "significantly altered" means some accommodation that requires a whole section to be removed, or the test to be heavily altered in some other way, and does not apply to just extra time or similarly regular adjustments.

A person seeking accommodations will still need to request them well in advance of the test from ETS, and will need to provide appropriate medical information in order for them to approve the request.