Paso Robles Merlot Grapes and Riesling Yeast?

I made a cider last year using a Wyeast Rudesheimer 4783 yeast strain. I decided this year to take it a step further and will add some grapes to the mix. My LHBS suggested a gallon bag of frozen Paso Robles Merlot grape must for the mix. I am not familiar with the grapes or winemaking. What do you think of the mix of local heirloom cider, merlot grapes, and Riesling yeast? Is there a better variety of yeast I should use?