Maybe. But, eventho the IC plays a key role in collecting intel re foreign threats to US elections, election security isn't one of the DNI's core responsibilities - that falls to DHS, FBI, and the states. Under EO 12333, the IC's core responsibilities are intel, and counterintel. 
So it could be that the concern goes more squarely to the IC's ability to provide accurate info about foreign plans, capabilities, & intentions. If the promise created pressure to provide damaging info no matter what (even if it's false) that wd undermine IC's fact-finding role.
From re-reading the various letters, it seems entirely possible that the WBer was concerned that the promise was made on terms or with conditions that would interfere with the IC's ability to do its job.
The possible scenarios are particularly complicated since there have long been public reports that Ukraine's security service, especially the unit responsible for investigating corruption cases, has been heavily infiltrated by/ is loyal to Russia's FSB.
I'll just repeat: even while so many facts have yet to emerge/ be confirmed, withholding from Congress a whistleblower complaint that the IG has found to be credible and urgent will do incalculable damage, near- and long-term.
