Custom logic to serialize a number as a set of symbols hardly comes near the threshold of "rolling your own crypto". So long as they follow a standard to generate the number, the serialization is basically irrelevant as long as it's reversible.
aside, the adage "don't roll your own crypto," has this funny side effect of homogenization where a weakness empowers an attacker against the maximum number of targets and makes mass interception more cost effective.
I've found that interoperability across diverse implementations is ironically the best protection against schemes that weaken rngs and key entropy to facilitate mass interception. independent implementations become a proof of a protocol or algorithm implementation. if there is only one functional implementation of something, it's where I would look first.