Yes that's probably a fair assumption at least. Note that the ripple is not a sine wave now so if your meter is doing the "rectify/filter/measure DC" and working backwards to AC it could be a bit off but it shouldn't be off by heaps. Best to look at with a scope if you've got one. If you've got a fast min/max function (which you probably don't if it's not True RMS) it might even catch it.

If you wanted to get *real* fancy/geeky you could rig a voltage divider to an ADC input and sample it with your CPU . You don't have to sample it particularly fast even.

At 5VDC and 3.3VDC you definitely don't want and shouldn't have any ripple. Still good to check on a DSO though if you have the means. There will be some switching noise at least on the 5V but should be pretty well filtered by the LDO.