I have some cache excange peers that also send me CSP cache. Seen in the debug logs as for example "0100:00000:SID". Can Oscam actually use this in any way to answer to clients or is this just plain useless unless fed back to some CSP instance?

AFAIK CSP uses ONID to and not provider-id but Oscam does not do aything with the ONID. For providers with ident 000000 I guess it's usable but for CAID 0100 does it have any use?