Absolutely say something... because the majority of babies *I know* (as in not a stat)... don't get burped during a feeding. They get burped afterward.
Some babies absolutely need to be (gerd, air gulpers, etc.), but the majority I have known don't... and it's a trick (burping in the middle) for gassy or colicy babies. BUT the flipside is that many babies will refuse to eat more after burping, and some react *abominably* to being interrupted (inconsolable screaming to the point of vomiting).
If your DCP is more used to non-colicky babies and babies who get *ticked* about being interupted, it may not even be on her radar. Especially if it takes a whole day's worth of feeding for any gassy crankiness to appear in the evening when the DCP doesn't have her, but you do.
I've taken care of lots of babies. My son was unique in all of them that he was a "marathon" burper. Meaning that I had to pat his back for nearly an hour after feeding each and every feeding. (I got good at reading a book one handed). First burp in the "normal" minute or two, and then monster burp after 45-60 minutes. The kind one can say a whole sentence in "burp". Seriously, crazy long burps, after seriously crazy long burping pats. But after a month of 24/7 care it was just "normal". I know most babies aren't like this, but even still, I would completely forget to mention it to a sitter or familiy member and then be shocked if they didn't do it. Even though it's totally "weird", for me it was normal. The whole "All babies are different, and we become experts only in our own" thing.