From a purely mechanical point of view the two effects would stack, as they do not conflict in any way.
Howls at the Moon gives
your Might Pool, +1 to your Might Edge, +2 to your
Speed Pool, and +1 to your Speed Edge
while Sculpt Flesh states
The damage dealt by the target’s
unarmed strikes increases to 4 points
From a more flavourful approach I can see how the two may seem to contradict. Sculpt Flesh and Howls at the Moon both bring about a physical transformation in the individual, and your thinking is that one change may or may not override the other.
What you need to remember is that just about every effect is brought about by nanites or similar Numenera devices/processes, and creating a ruling that Sculpt Flesh would stop working when a character transformed into beast form would just as likely stop other effects from working after the character had changed such as Adaptation or Resonance Field, both of which could be argued that they create a physical change in the individual that would also be overridden by the beast form change.
If there really is a problem with your group as to a consensus on this, the GM is always welcome to house rule that they do not work together, however cases like this should be rare.