There aren’t cap and roster limits in the offseason. If there were, 99% of teams would be in an illegal state, between loans no longer existing (they disappear on the last day of the regular season) and the 60-day DL disappearing.
I spoke to this a little bit here:
All teams are eligible to participate in arbitration. It is up to each league to determine how comfortable or uncomfortable they are with purposefully circumventing cap / roster rules towards the end of the regular season. There was a long debate in Slack a couple of years ago about the practice of starting 50+ auctions on the last possible day, and it basically comes down to whatever your league is ok with and setting expectations so everyone is on the same page.