...You can write software - but not for Mongoose Traveller by name (just as the OGL restricts the product identity for WoTC). That requires the Traveller Logo License, IIRC, which does explicitly restrict software.
Yep, I think that's what it comes down to.
Using the OGL for software for chargen would be pointless as the SRD leaves out critical elements like the careers and even the attribute basics, IIRC. You could make the software using all the rules - but not using unique names, including not stating any applicability to the trademarked names themselves. (Which is essentially the same as with copyright for U.S. games anyway - rules not being subject to copyright protection.)
Personally I'm not all that interested in automated character generation, but it is a problem for those who are. There are some third party career books for MGT though, so it might be worth contacting the publishers of those and see if they mind using their material instead.
Simon Hibbs