Both standards needed sleeves to be read.
For 3.5", yes. 5.25" disks could be removed from their protective enclosures, inserted into a drive, and used as normal. At least until the exposed medium was damaged by fingerprints or other debris. Not something you would normally do though. Source: Did it myself a few times mostly out of curiosity.
You’re thinking of component. The two are (or were) frequently mixed up.