Yes, make a reservation for the shuttle as soon as you get there. Know, however, if you get up early and show up and there's noone waiting they will take you over earlier than the res you made. There is also an Avis shuttle, that follows the same rule, no Avis customers, they take Radisson people. And, if the Radisson gets enough people needing the shuttle they are known to make a call to Disney to get them to come over and do a pickup or two as well. The one thing they collectively try to make sure of is everyone gets over there in good time.
Other tips:
The Radisson is a nice place to stay for the night, great pool.
They also have a nice Koi fish pond to just sit and relax by.
The breakfast buffet is also of good quality/quantity, they have a chef doing cook to order eggs.