Do hints improve memorization when using spaced repetition?
Short answer: Based on my assessment of the literature, I would say that a vague hint leaves room for retrieval practice, and will therefore likely elicit a testing effect. An obvious hint does not, and will therefore likely help recognition, but not recall.

Background

Spaced repetition refers to the practice of combining two well-known memory effects, namely the spacing effect and the testing effect, typically implemented in some form of flash cards. 

Testing effect

The testing effect aspect of spaced repetition is highly relevant. It refers to the finding that retrieval practice leads to improved long-term recall (cf. recognition) ability for a practiced item compared to non-practiced items. 

Modern theories on the testing effect tend to take the view that the testing effect represents a complex, active process in the brain rather than simple association formation or Hebbian learning. A critical meta-analysis of the recent testing effect literature unsurprisingly found support for the testing effect's existence, as well as some support for effortful processing as a contributing factor (Eisenkraemer, Jaeger and Stein, 2013). They did not find support for semantic elaboration theories (i.e., new/re-weighted brain associations).

Additional support for the testing effect as an active process comes from the fact that associated non-practiced items may be actively inhibited by retrieval practice, a phenomenon known as retrieval-induced forgetting (Anderson, Bjork and Bjork, 1994). We currently do not know much more than that the testing effect happens when we engage in retrieval practice. I know researchers who are studying exactly this, but at this point, I'm unfortunately not comfortable with discussing their thoughts or unpublished work. 

Spacing effect

I'm mostly including this for completeness' sake. The spacing effect was discovered by Herman Ebbinghaus in the 1880's and is one of the oldest phenomena studied in psychology. It refers to the tendency for animals to retain items presented over a longer period relatively better than when presentation of the same items is massed over a single brief period. It doesn't have any relation to the use of hints in spaced repetition learning, at least not one that I can think of.

References


Anderson, M. C., Bjork, R. A., &amp; Bjork, E. L. (1994). Remembering can cause forgetting: retrieval dynamics in long-term memory. Journal of Experimental Psychology: Learning, Memory, and Cognition, 20(5), 1063.
Eisenkraemer, R. E., Jaeger, A., &amp; Stein, L. M. (2013). A Systematic Review of the Testing Effect in Learning. Paidéia (Ribeirão Preto), 23(56), 397-406.