In my personal view, no it is not okay to nurture a political relationship with groups that represent ideas that I cannot abide.
I realise the conference under discussion is a political one, but I still find the idea that a group sponsoring a conference must be considered to be “nurtur[ing] a political relationship” with the other sponsors.
I go to a lot of conferences which are sponsored by various different groups, for example some have been sponsored by pharmaceutical companies. I never once assumed those sponsors were nurturing a relationship with one another. Indeed sometimes they are competitors. I assumed those organizing the conference asked different groups for sponsorship and received some from groups that perhaps hoped to have some influence by way of advertising their existence, but not necessarily by directly influencing what was said during the discussions.
I presume then, that “HandsUpScotland” wanted to organise a conference on this topic and then made requests for sponsorship from groups they thought might feel it was a useful discussion to have. There may be strings attached to the sponsorship, but I wouldn’t presume so, unless there is direct evidence of that. Even if there are strings (e.g. if each group gets a chance to provide a speaker) that doesn’t mean the entire conference is somehow tainted. Even if you choose to go to that lecture to see what the person says, that doesn’t mean you support or agree with their ideas. It means you want to hear what they have to say on a topic that interests you.
And yes, it is completely normal for diverse groups to come together to campaign on single issues. That’s politics for you. Very few issues are pushed through by small numbers, unless they have huge sums of money behind them. If a wide variety of groups all agree that one specific situation is morally wrong and they are willing to fight for it, they are much more likely to win that particular debate. Most political debates are won, in the long term, by persuading people your position is justified. If wider society believes that a law is unfair and unreasonable, the powers that be will ultimately not be able to enforce it, though driving changes, even to unjust laws, will generally take some time.
I also find it odd that you believe the pro-life stance is inherently anti-feminist. Feminism is a broad church. This idea that every feminist must have alignment of thought on every single issue affecting women is what puts many women off feminism altogether.