Hmmm, kind of. You technically have to go around and enter the security near Disneyland Hotel and the total walk time is just enough that you will be dreaming of staying at the Grand Cal as you walk that extra 10 to 15 min to the Westin if you feet are tired after a long day. It also makes mid-day trips back to the hotel less easy for those with little ones. With that said, the chances you can tailgate into the security gates and walk through the Grand Cal lobby and use those entrances into Downtown Disney or into GCA are high (I've never had to use my room key outside of very late evening/early morning hours on that left gate that leads up to the lobby), it always seemed to be open almost anytime there was decent foot traffic in the area.
How you should go -
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If you cut through -
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Saves you about 3 to 5 min of walking.