As far as I can tell, yes, you can.
Here's how I tested it out (hopefully, I understood your question): I turned off WiFi and 3G on my iPad1 (running iOS 5.0.1). I then went into the Calendar app, which is hooked into Gmail normally. I made a test entry on it for today. I also was able to scroll through the months and such to see other appointments already on my calendar - no problems.
I then turned back on my WiFi. I did see a spinning wheel icon in the upper left for a bit... I went to my iPhone, which also has my calendar hooked into the same Gmail account, and opened up the Calendar app. After a bit, that test appointment appeared on the iPhone.
Then, for the heck of it, I turned off the WiFi/3G again on the iPad. I then deleted the test appointment on the iPhone. I went back to the iPad and the test appointment was still there (obviously - no access). So, I turned on the iPad's WiFi. A few seconds later, that test appointment disappeared from the iPad.
So, I can only assume you can sync calendars across devices (at least those connected via Gmail). Note that I am not using iCloud or anything like that, just Gmail. But, I was able to see everything already in the calendar on the iPad without WiFi and I got near instantaneous updates.
I hope this reassures you. If I've somehow misunderstood your question, please let me know if there is anything else I can test for you. Good luck.
Marilyn
