Sorry Jay, I didn’t read your question carefully enough…
So the answer is no, you can’t have more than 10 inlets in an object.
(9 actually because the first inlet is always automatically given to you)
FYI: if you have access to the MaxMSP 4.5 SDK it can be inferred from there:
"Use intin() to create an inlet typed to receive only integers.
void intin (void *object, short index)
object: Your object. index: Location of the inlet from 1 to 9. 1 is immediately to the right of the leftmost inlet.
intin() creates integer inlets. It takes a pointer to your newly created object and an integer n, from 1 to 9. The number specifies the message type you’ll get, so you can distinguish one inlet from another. For example, an integer sent in inlet 1 will be of message type in1 and a floating point number sent in inlet 4 will be of type ft4. You use addinx and addftx to add methods to respond to these messages."