Indeed. Combo ports are there to better utilize switch chip present in device (e.g. if one doesn't need SFPs, he can use additional RJs). You can think of them as if they were solely SFP ports and you could plug in either optical SFP or RJ45 port SFP but not both at the same time. Only that with combo ports you have the RJ45 SFP implicitly plugged in at all times when optical SFP is missing.
In case of needed link redundancy, use 802.3ad link aggregation or similar. Many possibilities allow to use different kind of physical media for individual members of a bond (depends on implementation in the link partner). In some cases, when all links are operational, bond capacity is combined capacity of all members. When one link fails, bond remains operational with reduced capacity.