DNS records have a maximum length for each value, but TXT records may contain more than one value. That’s what you’re encountering here.
Apart from that: keep in mind that DNS records such as DKIM or SPF must be resolvable by the receiving mail server (e.g. when you send a mail from your domain to someone using a googlemail.com address, the Google mail servers will try to look up the DKIM record for your own domain). This in turn means that the records must be available from the public internet. It is unusual to have a UCS DNS server be reachable from the public internet, so let me ask you: are your UCS DNS servers reachable from the internet? Or are you at least using your UCS DNS as a master server for publicly reachable DNS slave servers?