There are some frogs that can be suitable for a day gecko enclosure, and there are some day geckos that are suitable for a frog enclosure, but not all frogs and not all day geckos are suitable for each other.
Mantella have been kept sucessully with certain day geckos. Both species are from Madagascar, and that is important. Day geckos that have been kept sucessfully with mantella include P. quadriocellata (and ssp) and P. laticauda (and ssp). Those day geckos are high tropical day geckos and can tolerate the high humdity that the mantella need. These are also smaller day geckos who will tolerate the mantella, where a P. madagascariensis grandis may not.
Finally, only someone with experience (with a capitol E) with day geckos and experience (with a bigger capitol E) with mantella should attempt this mix. This is a delicate mix and it is best handled by someone who knows what they are doing.