Management 'Guards' are highly unlikely to be doing anything other than hiding and trying very hard not to make complete tits of themselves, assuming they include those who have done a typical 'strikers' course of a few days and have barely any knowledge whatsoever. Or are GTR using only those who know what they're doing?
Some trains have guards on them... others have been DOO(P)+OBS over the last few strike days, whereas previously they were driver+guard (Three Bridges-Victoria via Redhill is the prime example of this).
With regards to the guards, the correct term for what you're thinking of is "contingency guards", as some aren't managers - for example, administrative staff, and a few who work in control centres but aren't required for their core operation. There are a fair few with experience and/or knowledge of the job - there are some who, for example, are conductor managers with the required competencies already, and quite a few of the safety and competency management team who've held conductor licences for ages. Then there are also station management and control staff who have various other safety-critical qualifications (such as dispatch licences) but have also trained as conductors for this. Of course, there are also exceptions to this, and I think there have been one or two tales posted on this forum before...
It should also be noted that one or two depots have a sizeable number of conductors who are not in the RMT and therefore have turned up at work, or have done so in order to be eligible for the voluntary severance/paying-off scheme. Where this is the case, some of these have crewed additional services, especially in the peaks, where the diagrams have effectively been composed from various bits of the "normal" timetable. So if you hear about random extra London Bridge-Horshams, as an example, those will probably be worked by regular conductors.