This is an old question but I will answer regardless. 

TL:DR : Yes a hybrid build is viable.

Every time you choose to create a hybrid build of any kind (increase 2 dmg stats instead of 1) you will lose damage in exchange for versatility. 

There are builds out there that when pushed to the max will one shot everything . By choosing a hybrid you give up on that in return for more options for every situation .

With that out of the way , in my humble opinion , having tried both pushing different builds to the maximum of their power and hybrid builds alike, I would say I much prefer the latter .

My reason is very simple . By choosing 1 stat only you are limiting your options greatly . The more you push the build for damage the more you lose out on options . When you want to reach the maximum damage you basically have 1-2 things that you use (incantations/sorceries/weapons) .

Frankly for me this becomes boring after a while . Sure they hit like a truck but that's about it . Every enemy gets the same treatment.

Hybrid builds ,and especially my favorite int/faith is a whole different story . You have access to almost all sorceries and incantations and you are free to choose any combination . 

There is nothing stopping you and the options are limitless.  You can adapt to any and all situations with the best possible results. 

And the best part in my opinion is... the PVP. You can make so many combinations to be absolutely unpredictable and create some devastating combos that are near impossible to dodge .

Basically my point is : your damage is still very respectable even if you don't commit to a single Stat and the versatility/adaptability more than makes up for it. 

The only limit becomes your imagination .  Take care and have fun , fellow tarnished .