In the particular case that you describe, using glDrawArrays will likely indeed be faster (or at least equally fast), since you cannot expect any benefit from the vertex cache, and you save a bit of bandwidth and cache memory (and 2-3 API calls) by not having to upload the indices in addition.
Also, possibly, it might be slightly faster to directly access vertex data in a strictly linear fashion than to go through an index only to result in the exact same access pattern afterwards. Though I'm sure GPUs have highly optimized specialized hardware paths to do just this exact thing at very little extra cost (no extra cost other than having more cache pressure).
However, even if it is not faster or even very slightly slower, it may still "make sense" to use indices, not for performance but because it may be more flexible. It depends on what you want to do.
Is there a reason why you do not share any vertices? That is very unusual. Are these a cloud of isolated triangles?
Edited by samoth, 05 November 2013 - 11:08 AM.