Believe it or not I think there's more 'grey' in Inquisition than you might think.
Vivienne certainly doesn't come off as a 'goody-two shoes'. She definitely seems willing to pull strings and find loopholes and would have no problem with the 'end justifying the means', especially if it elevates her own status.
Iron Bull likes to spend his days getting drunk and bedding anyone that won't break. He's loyal to the Qun, and the Qun, in our RL views, really isn't the most moral as it is militant and dark even. He comes off as admiring violence and even encouraging it if that means he gets to be a participant.
Sera's little phrase of 'maybe if we find someone who isn't so bad, he won't end up so dead' says a lot. She definitely seems willing to show no mercy and kill those she believes are wrong.
Cole is a spirit-assassin and a demon at that. That's all that needs to be said regarding him.
Varric's had his time in the underworld. Definitely more good than evil but isn't afraid to get Bianca dirty.
Dorian might be a renegade from his homeland but given his affinity for necromancy and status in Tevinter, he doesn't seem opposed to the darker side of magic. Plus personality wise he comes off as a bit narcissistic and vain.
Leliana's had her time as an Orlesian bard. She admits in Origins, if you harden her, that she enjoys killing. In fact she probably is involved in her line of work because she enjoys the subterfuge and death involved (maybe its just me but Leliana is a bit of a sociopath in my honest opinion, someone willing to be just about anyone). She's a covert assassin-agent in Inquisition.
Cullen can certainly be ruthless. He vouched for the Annulment in Origins and spent quite a bit of time on Meredith's side in DA2 (and Kirkwall's Circle was not the nicest to its inhabitants).
If anyone is straight-laced and 'paragon', I'm assuming it will be Cass, Blackwall, Josephine and Solas. And what we've seen of Cass she isn't afraid to break down doors, stab books and make threats. She's practically a renegade (paragade?) hero. Blackwall comes off as that protector/hero type (and I can be wrong on that too!). I do think Solas will be the nice guy though (probably the one that gets fed up with everyone else's antics). Josephine also comes off as a genuinely nice person. But she is also a noble and probably knows her way around the Grand Game (and likely has been a player in it herself).
And previous companions? The vast majority of ME's companions are certainly not straight-laced or goody-two shoes. Miranda is a stone-cold ice queen and teacher's pet of a human-supremacist black-ops organization. Jack is a psychopath. Garrus and Wrex are certainly the 'ends justify the means' type. Ashley and Zaeed are pretty brutal. Heck even Liara the 'nice girl/Betty/Aerie' type gets involved with the Shadow Broker. Sagacious Zu was morally neutral at best, Sky has had his time doing both good and bad, Silk Fox is certainly not opposed to using her status and position... : )