It is always possible to do a conscious xray on any animal. However not all patients are willing to sit still. I xrayed a dog conscious today and that was hard enough. Many vets will therefore suggest sedation/aneasthetic, because its much easier to work with a still/calm animal, even if its not the best for the animal. With personal experiece, although risky, general aneasthetics in piggies, if monitored closely by an experienced veterinary nurse can be fine and ive had several guinea pig aneasthetics go wonderfully, but unfortunally like cats and dogs it always varies from patient to patient.
Ive xrayed a guinea pig before which we gassed down with aneasthtic for only a matter of minutes, took xrays and it woke straight up. This may be an option, and gassing a piggie down for a matter of minutes (although sounds cruel to say) is a lot safer and has a smoother recovery in the majority of cases.
As for the lumps, without some sort of investigation, most easiest through either an xray or surgery there is no real telling. Maybe ask the vet about a fine needle aspirate biopsy. This is where a small needle is placed into the lump and a tiny sample of cells is taken. The sample can then be sent to the laboratory to see what kind of lump it is, benign or nasty. This may be an option, tho do be warned, tho you probably already know, guinea pigs are not a fan of needles. Bless them. Make sure you ask about the price of this too, lab fees can be quite expensive.
As for the ears, if your guinea was white I would have thought sunburn, but as hes not I really dont know what to suggest. Maybe some sort of moisteriser? Maybe ask your vet for something if theyre really bad. But if hes feeling under the weather in anyway this may just be related to feeling not so good.
I hope this helps a bit?
xx.