A sVDEV does not capture ARC. It stores all metadata on the sVDEV disks and if they are quick, it will help repopulate the ARC quickly as well. However, even SSDs are typically much slower than DRAM/ARC.
If you want the ARC to keep tracks of lots of files, I suggest making the ARC as big as possible (thereby limiting evictions) and limiting the instances of the machine being shut down. In practice, I doubt ARC being ‘preserved’ has all that much impact except in specific use cases.
The other way that the sVDEV speeds transactions is taking on small files, which HDDs struggle with. By default, the sVDEV is 75% allocated to small files, 25% to metadata. But you will want to tune your VDEVs and small-file cutoffs by use case and application. For example, you could force your sVDEV to host all VM / app datasets by aligning dataset recordsize and sVDEV small file cutoff. See the sVDEV resource for more info.